Basically, the steps like in bug 372724.
1) Select multiple layers
2) Start a long stroke (1000px colorsmudge brush is a good example)
3) Press Ctrl+E ***multiple*** times quickly
4) After all the background work is finished, press Ctrl+Z
There should be no crash, and the result should be somewhat expected.
Repeat the same for:
1) Merge down
2) Flatten Image
3) Flatten Layer
4) Transform a layer using "Layers" menu(?)