I've noticed a problem with the Move to Quarantine function: if the file is in use and cannot be deleted, it is copied instead. ClamWin still reports it as Moved, though. This is obviously problematic.

Please fix it.

alch do u quarantine direcly from clamwin or using the move option of clamscan? I should anyway check if the native port correcly moves readonly files.
For "in-use" files is another story
yes I'm a bit off topic but you remembered me to check this in my native port

it uses clamscan --move