Waiting imps always hold a slot, and slots empty together
Waiting imps always take a slot. Before, tapping quickly could send groups after tiles that were still being mined, and they stood around outside the slots in an invisible queue.
A tile an imp is already mining counts as taken. Imps of that color with nothing else to reach wait in a slot.
When the mining stops, every waiting group with a tile to reach leaves its slot at the same moment, instead of one slot after another from left to right.
The levels got harder under the stricter rule. All 12 are still proven winnable, and the order was adjusted so difficulty still rises.
TREASURE!