Description:
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This affects all versions with gc, 5.3 to 5.5
Tried script on http://3v4l.org/KmGDj

I can't tell what happens internally, but it looks like garbage collector will not detect and collect circular dependencies if there are SPL classes involved (i suspect other built-in classes are affected too)

Test script:
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https://gist.github.com/Xerkus/7562464/raw/f6d0ff3f1fbc24a3a3ca99ac974571748103ab51/test.php

Expected result:
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Memory stays at about the same level

Actual result:
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Used memory grows constantly