This is indeed a strange one. I would love to help out on this one however, I will also need your help on the matter if you don't mind.
Would you please describe exactly the steps you take to produce this issue.
Are you facing this issue on ARCHICAD 21 or on a newer ARCHICAD version?
If you could provide me with the file you are experiencing this issue on via PM, then we can investigate this at length.
I hope to hear back from you soon.
Have a great day!