diff --git a/inc/cleantalk-public.php b/inc/cleantalk-public.php
index d141014c2..863a05663 100644
--- a/inc/cleantalk-public.php
+++ b/inc/cleantalk-public.php
@@ -409,9 +409,28 @@ function apbct_sgo_bypass_query_params($bypass_query_params)
     return $bypass_query_params;
 }
 
+/**
+ * Nesting level of the buffer opened by apbct_buffer__start().
+ *
+ * @param int|null $set
+ *
+ * @return int
+ */
+function apbct_buffer__own_level($set = null)
+{
+    static $level = 0;
+
+    if ( $set !== null ) {
+        $level = (int)$set;
+    }
+
+    return $level;
+}
+
 function apbct_buffer__start()
 {
     ob_start();
+    apbct_buffer__own_level(ob_get_level());
 }
 
 function apbct_buffer__end()
@@ -421,6 +440,19 @@ function apbct_buffer__end()
     }
 
     global $apbct;
+
+    // Buffers opened after ours (WP late-printed styles hoisting, other plugins) must be flushed,
+    // not discarded — otherwise their replacements never reach the output.
+    $own_level = apbct_buffer__own_level();
+    if ( $own_level > 0 ) {
+        while ( ob_get_level() > $own_level ) {
+            $previous_level = ob_get_level();
+            if ( ! @ob_end_flush() || ob_get_level() >= $previous_level ) {
+                break;
+            }
+        }
+    }
+
     $apbct->buffer = ob_get_contents();
     ob_end_clean();
 }
diff --git a/tests/Inc/TestCleantalkPublicBuffer.php b/tests/Inc/TestCleantalkPublicBuffer.php
new file mode 100644
index 000000000..679f3176b
--- /dev/null
+++ b/tests/Inc/TestCleantalkPublicBuffer.php
@@ -0,0 +1,119 @@
+<?php
+
+namespace Inc;
+
+use Cleantalk\ApbctWP\State;
+use PHPUnit\Framework\TestCase;
+
+class TestCleantalkPublicBuffer extends TestCase
+{
+    /**
+     * @var int Output buffering level owned by PHPUnit, must be restored after every test.
+     */
+    private $level_before;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        global $apbct;
+        $apbct = new State('cleantalk', array('settings', 'data', 'errors', 'remote_calls', 'stats', 'fw_stats'));
+        $this->level_before = ob_get_level();
+    }
+
+    protected function tearDown(): void
+    {
+        while ( ob_get_level() > $this->level_before ) {
+            ob_end_clean();
+        }
+
+        global $apbct;
+        unset($apbct);
+        parent::tearDown();
+    }
+
+    public function testBufferEndCapturesOwnBufferAndLeavesTheOuterOneOpen()
+    {
+        global $apbct;
+
+        ob_start();
+        echo 'OUTER;';
+        $outer_level = ob_get_level();
+
+        apbct_buffer__start();
+        echo 'PAGE;';
+
+        apbct_buffer__end();
+
+        $this->assertSame('PAGE;', $apbct->buffer);
+        $this->assertSame($outer_level, ob_get_level());
+        $this->assertSame('OUTER;', ob_get_contents());
+
+        ob_end_clean();
+    }
+
+    public function testBufferStartRecordsItsOwnNestingLevel()
+    {
+        ob_start();
+
+        apbct_buffer__start();
+
+        $this->assertSame(ob_get_level(), apbct_buffer__own_level());
+
+        apbct_buffer__end();
+        ob_end_clean();
+    }
+
+    public function testBufferEndFlushesNestedBuffersAndAppliesTheirCallbacks()
+    {
+        global $apbct;
+
+        ob_start();
+        echo 'OUTER;';
+        $outer_level = ob_get_level();
+
+        apbct_buffer__start();
+        echo 'HEAD:PLACEHOLDER;';
+
+        // Emulates WP late-printed styles hoisting: a buffer opened after ours that replaces
+        // its own content only when it is flushed.
+        ob_start(static function ($chunk) {
+            return str_replace('PLACEHOLDER', 'REAL_CSS', $chunk);
+        });
+        echo 'BODY:PLACEHOLDER;';
+
+        ob_start();
+        echo 'FOOTER;';
+
+        apbct_buffer__end();
+
+        $this->assertSame('HEAD:PLACEHOLDER;BODY:REAL_CSS;FOOTER;', $apbct->buffer);
+        $this->assertSame($outer_level, ob_get_level());
+        $this->assertSame('OUTER;', ob_get_contents());
+
+        ob_end_clean();
+    }
+
+    public function testBufferEndDoesNotLeakPageContentIntoTheOuterBuffer()
+    {
+        global $apbct;
+
+        ob_start();
+        echo 'OUTER;';
+
+        apbct_buffer__start();
+        echo 'PAGE;';
+        ob_start();
+        echo 'NESTED;';
+
+        apbct_buffer__end();
+
+        $outer_content = ob_get_contents();
+
+        $this->assertSame('OUTER;', $outer_content);
+        $this->assertStringNotContainsString('PAGE;', $outer_content);
+        $this->assertStringNotContainsString('NESTED;', $outer_content);
+        $this->assertSame('PAGE;NESTED;', $apbct->buffer);
+
+        ob_end_clean();
+    }
+}