[6.11.15] Moving files ETA and progress goes up to 99% then down to 50%

Progress window in file manager reports completely random numbers

It reports 99% completed, ETA of a few minutes, and then when moving subfolder goes down to much lower number (56% here), ETA goes up by a lot.

It feels like ETA and completion progress is not calculated for over main folder size but only for each subfolder

How to repeat:

Move a large (hundreds of GB) folder with a few subfolders containing a lot of small files (photos) and some big ones (videos).

Just before taking this screenshot UNRAID reported 99% progress and 7s seconds, which obviously was incorrect as it just started moving huge folder.