Same problem here... mcrypt_generic_init works fine, but mcrypt_generic_deinit gives me 'Fatal error: Call to undefined function: mcrypt_generic_deinit()'. Running v4.3.1 on W2K, and the v4.3 mcrypt stuff from http://ftp.proventum.net/pub/php/win32/misc/mcrypt/ . It's definitely an exported symbol in the libmcrypt.dll, so I expect it's something on the PHP side that's the problem...
EDIT: Maybe it's this: http://bugs.php.net/bug.php?id=22520
Will report back.
EDIT2: Yeah... I copied the mcrypt extension dll from the snapshot over the top of the old one and now it works fine.