1. Let lemming spawn from hatch.
2. Highlight the lemming. (Arrow shown over its head.)
3. Framestep-back to a time when the lemming is still in the hatch. It doesn't matter whether it would spawn in exactly 1 frame from now, or if the spawn will happen in several frames only.
4. Highlight-skill-assign floater. (This means: You hold the highlight key, and meanwhile, click the floater icon in the panel.) Observe how the skill sound plays, and a floater is deducted from the panel. You can assign many floaters.
5. Highlight-skill-assign exploder. Sound plays, you can assign many exploders.
6. Highlight-skill-assign climber. The game blocks these assignments, nothing deducted in the panel, no sound.
7. Unpause and let play. Observe how the lemming is neither floater nor exploder.
8. Framestep back and forth. "INVALID" flashes in the panel where the current activity of hovered lemming would be shown.
Expected instead: No assignments go through while lemming in hatch. INVALID never shown in panel.
Tested in the no-fading build, which shows 1.44n in the main menu.
-- Simon
It seems this is already fixed in the experimental versions. We'll leave this topic here in case anyone discovers that some situations still allow it to happen.