So, what's the matter? Well, the web-based calendar runs perfectly, but sometimes Android messes up: some calendars, which are correctly shown in Google Calendar, do not appear in Android. Repeating the synchronization does not fix a thing, you have to get dirtier than this.
Go to Settings > Applications > Manage Applications > Running > Calendar storage
Then, click "Clear data" and "Force stop". The first one wipes out the local cache; the latter forces the calendar to restart and download the calendars again from the internet.