Download and Delete Doesn't Use Queue

If I select multiple files and download with f5, it download multiple files simultaneously using all the queue slots.
However, if I download and delete with f6, it downloads one file at a time.
Is this a bug or design?
If latter, is that possible to download and delete multiple files simultaneously using all the available queue slots?
WinSCP 5.15.3 Portable
Windows 10 pro 64-bit v1903
SFTP
Commander

It's by design:
https://winscp.net/eng/docs/ui_pref_background#fn1