Why does the iCloud PC app window constantly 'pop up'?

I've been using iCloud PC for some time, just to synchronise my Calendar entries on my Macbook, iPhone and work (Windows 7) PC. With the latest incarnation of iCloud PC (not sure what version number, there's a small '5.0' showing in the top rhs of the iCloud control screen, not sure if this is a version number?), the iCloud control app seems to 'pop up' every few minutes, which is a joke. Previously, the app just ran in the background - now, if I hit 'close', the window clears down, but then re-appears some short time afterwards. The only way I can prevent this is to 'log out' if iCloud completely, with the option either to retain (in archive) or delete the iCloud files. This is a total pain and renders the application effectively useless. Anyone know of this problem, is it a bug in the latest version? Many thanks!