Description:
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could be related to #24121

have a site wich use outout buffering (ob_start("callback") (in the callback funktion i do some str_replace 's ) in 4.3.1 it worked perfekt.

in 4.3.2 it does not work. it seems the callback funktion is not called.

if you need further information let me know.

Reproduce code:
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function callback($buffer){
$buffer2=$buffer;
$buffer2=str_replace("%TITLE%","asdfadsf",$buffer2);
return $buffer2;
}