5.6Version mcrypt_cbc can't use and Mcrypt_generic encrypted results are sometimes inconsistent

Hello PHP : 5.6Version mcrypt_cbc can't use and Mcrypt_generic encrypted results are sometimes inconsistent Mcrypt_cbc PHP5.6 version were abandoned, by our customers using version 5.3, resulting in version 5.6 we encryption and decryption could not be agreed with the customer, but we cannot require that clients must be upgraded to version 5.6, how tosolve this problem? We try to use the alternative function mcrypt_generic in some cases are the same, but in some cases encryption and decryption to inconsistent results. Hope the lawsuit will give a solution, project affected is large. Thank you very much!!!