How to reproduce:
Open program, try to move columns in order to change their width (make them smaller or broader).

Actual behavior:
The limits between the columns are not individually movable (no double arrow, which is usually used to move the limits of boxes and windows, appears); columns stay in the pre-set width.

Expected behavior:
When the cursor is near the limits, the "double arrow" appears and you can move the limits of the columns in order to change their width.
This should be possible for all three columns that are part of the UI.