Subject messes up and reappears in Outlook Calendar

case 1
My colleague has delegated right for his calendar to me. Someone has
invited him to a meeting but amend it later. I could see the updated at the
beginning. However, later the subject has been changed to some unrecognized
characters.

case 2
Someone has invited my colleague to a meeting but he has cancelled it later.
I could see that the meeting has been removed from his calendar. However,
later the meeting reappears on his calendar, but it was marked with "deleted".

Did any one encounter the similiar problem in calendar? Is there a way to
resolve it since it is very confusing? Thank you very much!