Same problem here!
is your Hotmail account set up as Exchange/using the Exchange Web Services protocol?
If not, then you are not synchronizing your calendar to the server at all and your event are probably being saved in the Local folders.
Please check if you have this setup in Menu>Tools>Accounts section.
If not, please set up your account as such. Just click the New account option and choose Mail>Exchange.
Use your mail address for both the ‘Email’ and ‘Username’ fields.