Steps to reproduce:
1. Place a pickup skill, entrance or exit
2. Edit the skill count or lemming count by typing in a value (not by using the up/down clickable buttons or arrow keys)
3. Click in the level area such that the pickup skill / entrance / exit is de-selected
The change does not get applied, and an error message pops up.
Workaround: Click somewhere that doesn't deselect the object first. This could be another edit field (like the skill checkboxes), or clicking in the level area somewhere that doesn't deselect the object.
