Description:
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I have a pregex that starts looks like this:

/(?:<p.*?>)?\[.../s

(The last ... is to be interpreted as an ellipsis)

Removing the /s or the <p> tag before the \[ fixes the problem. Otherwise the preg_replace_callback() returns an empty string and never calls the callback. This is the case with several pages of data we have, although it is not easy for me to determine what triggers the problem.

P.S. If the callback does not exist, the function has a shortcut and the input is immediately returned as is.

Reproduce code:
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1740 lines of code found as an attachment to that page:

http://linux.m2osw.com/pcre_php_s_modifier_bug

The main reason for the length is the HTML code, the failing code is just 1 line at the bottom.


Expected result:
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($s == preg_replace_callback(...)) === TRUE

since the callback should not be called with that HTML.

Actual result:
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preg_replace_callback() returns NULL