Patch is mostly created by script in egroupware/doc/fix_depricated.php in separate commit.
I do NOT advice to apply this patch to a production system (it's commited to trunk!), as the automatic modified regular expressions have a good change to break something ...
child, that has executed a php script with mbstring.func_overload=7 once, will
overload substr() in a later execution of another php script, even if the
Location context of that script has mbstring.func_overload=0 set. Since the
WBXML decoder works byte-by-byte to determine substring length, it fails, if
mb_substr() is used. This patch prevents this.