Some calendar appointments (those received from a POP email address different from my live.com account) register correctly in Outlook 2013 (on Windows 8.1 Pro) but do not sync to my Outlook.com Calendar. Calendar entries made manually on Outlook 2013 calendar sync correctly, as do any accepted meeting requests received directly to my live.com email account (although meeting requests forwarded to my live.com address from my other account do not sync when Accepted but do register correctly on my local Outlook 2013 calendar).

My wife has the same issue with the same configuration on a different machine so the issue is not account related, nor is it related to a mailbox corruption.

Searching online shows others reporting the same issue (for some months now) but I have not found a solution. Please can you point me to a solution to this serious problem.