glitching characters

sometimes when i start minecraft, all the characters are glitchy! i already found a solution so it goes back to normal: first, i set minecraft to the default resource pack. (because when i dont do that, it wont help) and then i delete the 1.6.1 version, and install that version again. and then its normal again. but after i started minecraft a few times, it just happens again! i hope you guys can fix this bug.