Scratch

In the original Scratch program, the Ask and Wait prompt would disappear if the script that created stopped. But in the online players (including the prototype, IIRC) it stays visible even though answering it won't doing anything that point. In future versions, I think the prompt should consistently disappear as it does now in the offline player.

Alternatively, there could be a block to explicitly tell the prompt to close, but that seems like overkill.

See this project for an example:
http://scratch.mit.edu/projects/ManaUser/2571341
Notice what happens if you let the time run out.