Option 'rescan cache when new definitions load' cannot be disabled

SEPM 12.1.RU5 (Win Server 2003), clients mixed 12.1.RU5 / v12.1.4.1a.RU4 MP1 (Win XP/Win 7), all OS fully updated. One of the RU4 clients has unusually high HD I/O activity, with ccSvcHst.exe as a culprit. I researched a bit through a forum and found out that cache rescans could be the reason for that.

Tried to disable 'rescan cache when new definitions load' option in Policies / Virus and Spyware Protection / [affected clients policy] / Auto-Protect / Advanced / File Cache... but it doesn't stay disabled, policy changes not saved and not propagated. Tried in the rest of my policies, even made new one from default, the same. None of the changes made in File Cache window are being saved/communicated.

Anyone else seeing this behavior?

Thanks