diff --git a/src/DependencyInjection/ContainerFactory.php b/src/DependencyInjection/ContainerFactory.php
index 67f8d4ea1a..9d5c312368 100644
--- a/src/DependencyInjection/ContainerFactory.php
+++ b/src/DependencyInjection/ContainerFactory.php
@@ -172,29 +172,34 @@ public function create(
 	public static function postInitializeContainer(Container $container): void
 	{
 		$containerId = spl_object_id($container);
-		if ($containerId === self::$lastInitializedContainerId) {
-			return;
-		}
-
-		self::$lastInitializedContainerId = $containerId;
-
-		/** @var SourceLocator $sourceLocator */
-		$sourceLocator = $container->getService('betterReflectionSourceLocator');
 
-		/** @var Reflector $reflector */
-		$reflector = $container->getService('betterReflectionReflector');
-
-		/** @var Parser $phpParser */
-		$phpParser = $container->getService('phpParserDecorator');
-
-		BetterReflection::populate(
-			$container->getByType(PhpVersion::class)->getVersionId(),
-			$sourceLocator,
-			$reflector,
-			$phpParser,
-			$container->getByType(PhpStormStubsSourceStubber::class),
-			$container->getByType(Printer::class),
-		);
+		// Populating BetterReflection wires up global static state in the BetterReflection
+		// facade, so it only needs to run once per container. The remaining global state below
+		// (static accessors, caches, feature toggles) can be mutated by other containers,
+		// tests or data providers in the meantime, so it must be re-applied on every call -
+		// even when returning to a container that was already populated. Otherwise unrelated
+		// tests sharing the same container leak global state into each other.
+		if ($containerId !== self::$lastInitializedContainerId) {
+			self::$lastInitializedContainerId = $containerId;
+
+			/** @var SourceLocator $sourceLocator */
+			$sourceLocator = $container->getService('betterReflectionSourceLocator');
+
+			/** @var Reflector $reflector */
+			$reflector = $container->getService('betterReflectionReflector');
+
+			/** @var Parser $phpParser */
+			$phpParser = $container->getService('phpParserDecorator');
+
+			BetterReflection::populate(
+				$container->getByType(PhpVersion::class)->getVersionId(),
+				$sourceLocator,
+				$reflector,
+				$phpParser,
+				$container->getByType(PhpStormStubsSourceStubber::class),
+				$container->getByType(Printer::class),
+			);
+		}
 
 		ReflectionProviderStaticAccessor::registerInstance($container->getByType(ReflectionProvider::class));
 		PhpVersionStaticAccessor::registerInstance($container->getByType(PhpVersion::class));
diff --git a/tests/PHPStan/DependencyInjection/ContainerFactoryPostInitializeTest.php b/tests/PHPStan/DependencyInjection/ContainerFactoryPostInitializeTest.php
new file mode 100644
index 0000000000..a3494bef63
--- /dev/null
+++ b/tests/PHPStan/DependencyInjection/ContainerFactoryPostInitializeTest.php
@@ -0,0 +1,87 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\DependencyInjection;
+
+use Override;
+use PHPStan\File\FileHelper;
+use PHPStan\Php\PhpVersion;
+use PHPStan\Reflection\PhpVersionStaticAccessor;
+use PHPStan\Reflection\ReflectionProvider;
+use PHPStan\Reflection\ReflectionProviderStaticAccessor;
+use PHPStan\Testing\PHPStanTestCase;
+use function sys_get_temp_dir;
+
+final class ContainerFactoryPostInitializeTest extends PHPStanTestCase
+{
+
+	private bool $bleedingEdgeBackup;
+
+	private PhpVersion $phpVersionBackup;
+
+	private ReflectionProvider $reflectionProviderBackup;
+
+	#[Override]
+	protected function setUp(): void
+	{
+		$this->bleedingEdgeBackup = BleedingEdgeToggle::isBleedingEdge();
+		$this->phpVersionBackup = PhpVersionStaticAccessor::getInstance();
+		$this->reflectionProviderBackup = ReflectionProviderStaticAccessor::getInstance();
+	}
+
+	#[Override]
+	protected function tearDown(): void
+	{
+		BleedingEdgeToggle::setBleedingEdge($this->bleedingEdgeBackup);
+		PhpVersionStaticAccessor::registerInstance($this->phpVersionBackup);
+		ReflectionProviderStaticAccessor::registerInstance($this->reflectionProviderBackup);
+	}
+
+	public function testReappliesGlobalStateForAlreadyInitializedContainer(): void
+	{
+		// A separate container whose ReflectionProvider stands in for state leaked by an
+		// unrelated test. Building it also makes it the "last initialized" container.
+		$leakedReflectionProvider = $this->createSeparateReflectionProvider();
+
+		$container = self::getContainer();
+
+		// Make this container the last initialized one again, so the final
+		// postInitializeContainer() call below exercises the early-return guard.
+		ContainerFactory::postInitializeContainer($container);
+
+		$expectedBleedingEdge = BleedingEdgeToggle::isBleedingEdge();
+		$expectedPhpVersion = $container->getByType(PhpVersion::class);
+		$expectedReflectionProvider = $container->getByType(ReflectionProvider::class);
+
+		self::assertNotSame($expectedReflectionProvider, $leakedReflectionProvider);
+
+		// Simulate another test / data provider leaking global state while this container
+		// stays the "last initialized" one (e.g. two test classes sharing the same container).
+		BleedingEdgeToggle::setBleedingEdge(!$expectedBleedingEdge);
+		PhpVersionStaticAccessor::registerInstance(new PhpVersion(70100));
+		ReflectionProviderStaticAccessor::registerInstance($leakedReflectionProvider);
+
+		// Returning to the same container must restore all global state, even though the
+		// expensive BetterReflection population is skipped for an already-initialized container.
+		ContainerFactory::postInitializeContainer($container);
+
+		self::assertSame($expectedBleedingEdge, BleedingEdgeToggle::isBleedingEdge());
+		self::assertSame($expectedPhpVersion->getVersionId(), PhpVersionStaticAccessor::getInstance()->getVersionId());
+		self::assertSame($expectedReflectionProvider, ReflectionProviderStaticAccessor::getInstance());
+	}
+
+	private function createSeparateReflectionProvider(): ReflectionProvider
+	{
+		$rootDir = __DIR__ . '/../../..';
+		$fileHelper = new FileHelper($rootDir);
+		$rootDir = $fileHelper->normalizePath($rootDir, '/');
+		$containerFactory = new ContainerFactory($rootDir);
+		$tmpDir = sys_get_temp_dir() . '/phpstan-tests';
+		$container = $containerFactory->create($tmpDir, [
+			$containerFactory->getConfigDirectory() . '/config.level8.neon',
+			__DIR__ . '/../../../src/Testing/TestCase.neon',
+		], []);
+
+		return $container->getByType(ReflectionProvider::class);
+	}
+
+}