I often look at information in tables from CCleaner and found an unpleasant feature of their display.
If I change the size of the column to see the full file name or path or other information, then after a couple of seconds the column size will automatically decrease to default.
For example, while searching for duplicates - "Tools" -> "Duplicate Finder" -> [Search]:
Your screenshot shows that the duplicate search is still running. (Rotating circle in the status bar).
It will resize as you show whilst the tool is still searching and finding duplicates.
Each time it finds new duplicates it will write them to the list, which refreshes the list and so resizes it.
Wait until the tool has found all the duplicates and then resize the column, it should then stay resized.
So not realy a bug as such, but could be an improvement if they can stop it from happening and keep the column width across refreshes.