I thought I had this problem when my player decided to do a disk check RIGHT AFTER I installed HiJack. When I installed HiJack, the first thing I did was disable the disk check. A few minutes later, I did a sync and a disk check started. At first, I said "what the heck?" until I remembered that the instruction to perform a disc check was made during my PREVIOUS sync BEFORE I installed Hijack.

IIRC, when the player (or emplode?) decides a sync is needed because of a certain amount of time or a certain number of consecutive syncs, it doesn't happen right away. Instead, it sets itself up so that upon the NEXT sync, a disc check is performed.