Using "copy"/"cut" and "paste" in cloud file browser only working once

I noticed a problem copying or moving files within the same library. The first time it works flawlessly. The file is small (22 kB) and appears to be copied instantly. But, when trying the same thing with another file afterwards, I get the error “Another copy or move operation is in progress. Please wait until it finishes.” I have waited quite some time now. On seahub I can assure the first file has been transfered all right.

I see no messages in any of the server-logs.

Seafile Client 8.0.6
Seafile Server 8.0.17