OWA 2013 Appointment will disapear during checking e-mail

Dear Microsoft users,

I'm working at a school with 600 teachers. I received a question about the next problem:

I'm making an appointment in OWA 2013. I'm writing some text etc. and in the meanwhile I receive an e-mail.

I switch directly to the e-mail option to read my e-mail but if I go back to my calendar, the appointment what I made is gone.

I have to create a new appointent.

Is there a solution for this?

I tried already a workaround and the only solution what I found was to open "Event" so an extra popup is coming up.

This is a little frustrating.

I hope toe hear from you.

Kind of regards,

Roderik de Haar