Is there a particular distance from the top of the win that you need to place blocks? For example, I had the win, an empty space above it, and a stone block above that... and when I play-tested it, the win triggered by itself. Do there need to be at least two empty spaces above the win? Or is it just my device?
Hmm, something doesn't seem right. Would you be able to share your troublesome card with us here? I've attached a copy of a card that I believe depicts your situation without the win auto-triggering. Is yours different somehow that could help us debug the situation?
I've tried to replicate the problem and have been unable to. However, I've rebooted my tablet since then, and it was a level I was working on for a few hours, so now I'm guessing that it was a memory glitch that caused the problem. (shrug)