Description:
------------
Use of call_user_func (or call_user_func_array) crashes if apd 
is enabled, when called function returns.

Reproduce code:
---------------
The following line crashes with apd enabled:

return call_user_func(array($this->peerName, 'doCount'), $this->criteria);

If I change the line to:

return eval("{$this->peerName}::doCount(\$this->criteria)");

It works.

-OR- 

If I disable the apd extension, it works.

Interestingly, it's not the CALL that causes the segfault. The called function executes. It is only when the called function RETURNS that the segfault occurs.

Expected result:
----------------
Should not crash...

Actual result:
--------------
segfault. this occurs on a production machine and I only have 
5.1.6 on the production machine, so I cannot give you a 
backtrace, sorry. Hopefully this can be easily reproduced.