I have noticed that the incoming call in this case is not marked as Rejected or Answered, but similar to Silenced. When I end up to Conversations app in answering call it is yet possible to answer to an incoming call - I close Conversations app, open a Phone app and can answer the same call which I missed due to screen glitch.
Screen glitch has been occured when Phone app is set to be in Portrait or Automatic without auto rotation. Haven't tried Landscape mode yet as it's unconvinient to hold the phone in this way.

PS Apps installed only from maemo-extras