Hi Alex,
I've been trying today to reproduce this issue so I can properly fix it, though it seems to have mysteriously disappeared for me.
I'm wondering if you have any other way to reproduce it in v1.33b? I've tried using the code you've described above and also through manipulating a few things in a checked out copy of Umbraco, and it always seems to build fine.
I'm starting to wonder if perhaps it was actually a symptom of another issue already fixed ...
Cheers,
Remco