Synchronisation problem on iPhone device (iOS7) and iCloud, Synchronisation problem on iPhone device (iOS7) and iCloud

It is not a problem, but intended behavior. Device is only going to sync with one account. It will receive mail to another, but that is where it ends.

FYI, you can sync multiple iCloud accounts on the same device by adding them in Settings>Mail,Contacts,Calendars>Add Account>iCloud and signing in with separate IDs. These "secondary accounts" will sync mail (fetch), contacts, calendars, reminders and notes. See http://support.apple.com/kb/TS4020. Families often find this convenient as it allows them to maintain separate data sets, while maintaining a shared calendar or contacts (http://www.ilounge.com/index.php/articles/comments/sharing-itunes-icloud-account s-in-a-family/).

Thank you Randers as always, nice addition to stuff I do not know. There is note in that article that may explain why it does not work for OP. So if secondary account was added without certain categories of data inside - say calendars - that particular category would not sync at all or sync properly, like he described?

"Secondary accounts should only be set up if you already have mail, notes, contacts, calendar, or reminders data in another account that is separate from your primary account."

That's true but I couldn't tell if the OP was syncing calendars in the primary account or not. However, the fact that adding the event to the calendar in the secondary account on the phone causes it to appear on icloud.com but disappear from the phone suggests that it is syncing with iCloud. Makes me wonder if the event may have been added to the calendar in the past and the iOS devices are only set to sync events that are 1 month or 2 weeks old. If an event was then added to a date that preceeded the sync date setting, it that would cause it to sync to iCloud (and appear on icloud.com) but immediately disappear from the iOS devices.

I am making a bet that last explanation is wrong - my impression of OP is a bit more evolved.