Massimo, I know that clockpick is not everyone's favourite, but until something better comes... I wonder whether you would consider updating it from 1.24 to 1.28 in calendar.js?
The upgrade corrects a couple of issues that have been causing problems. Only thing to watch for is that the old CSS clauses all include z- index:99; but the latest version does not, so you might have to make sure these are in to make it work. Otherwise it seems to be fine. Many thanks! David