Hi,
when I change the project of an activity, the activity appears within activities list of the new project;
but not in the planning view, it remains in the planning view of the first project!!
Regards
Could you detail use case steps by steps ? On which screen do you operate ?
(show print screen)
Which version of ProjeQtOr ?
Can you check WBS for activity before and after ?
[Edit] I just tested and it's working as expected, so either you work on old version or it is a misunderstanding on "change project" or you used specific method that I did not think about.