I "HAD" this exact issue with 4.1.5, 4.1.6 and 4.1.6 MR1. On devices running firmware 184.108.40.206 and older the calendar sync, when disabled on the device would re-enable during server reboots causing all kinda of calendar hell for users who sync to a different calendar in Desktop Manager. 220.127.116.11+ on the device solved this problem as sync settings from the server are ignored by the device if set to disable.
We have no 7xxx devices and all of my 8xxx (we have ALL of them) devices now run beween 18.104.22.168-22.214.171.124. Thanks RIM. Your the best. :(