Progress bar in nautilus dock icon not restored after locking->unlocking screen

Observed in Unbuntu 18.04 and Ubuntu 16.04.6 LTS

When copying a substantial amount of files, that will take some time, a progress bar appears in the nautilus icon in the desktop dock.
Normally that progress bar disappears when the file copy task is done.
However, locking and unlocking the screen while the file copy task is still busy, will also cause the progress bar to disappear.
But that is not correct since the file copy task is not done yet.

For me this led to loss of data, as I was lead to believe that the copy process was done, and I started to remove the files I thought were copied.

I expected to see a progress bar in the nautilus icon, as I saw it before the screen was locked,since the copy action was not finished yet.
But the progress bar was gone. Just the bare nautilus ("Files") icon.

I checked if this was "normal" behavior for an icon with a progress bar.
For this I used the archive manager to compress a large folder.
Verified that there appeared an archive manager icon containing a progress bar, locked the screen, unlocked the screen, checked the archive manager icon and it still had a progress bar.

For the nautilus icon this is not the case, the progress bar in the icon is not restored, even though the copy action is still ongoing.

nautilus:
  Installed: 1:3.18.4.is.3.14.3-0ubuntu6