Kmail IMAP problems

Last week I complained about IMAP problems with Kmail. I've tried to increase mail checking interval but it doesn't seem to have helped a lot. Kmail crashes a few times a day and Kontact refuses to start again from time to time. To make things even worse this week, Korganizer is getting confused over disconnected IMAP storage and often prompting me to resolve synchronization problems. I think it worked much better with 3.5.2...