UPDATE: Here's how I think you can reproduce the behavior:
1. Open b4a, preferably a couple instances
2. click "Designer" in menu bar. designer and abstract designer should both pop up
3. switch to the other b4a instance, or another program
4. use window's task manager (i.e. task bar) to go to "designer" window of first project
5. click "tools-show abstract designer"
6. BINGO