I've got a (non-blocking) issue on imputations forms for my resources: when a resource has an expired affectation to a project, he/she continues to see some activities of this project in his/her timesheet ... but not the project. Thus the resource sees "orphan" activities (although they're really linked to the project).
This seem to be a display issue.
I tried again to reproduce your issue, without success.
Can you please try and reproduce on Demo ?