This is an interpreter bug, not a bug in the Inform compiler. But it showed up in several interpreters – pretty much every interpreter except the Mac one – so I wanted to post a quick summary.
Quick summary: if you try to write to an external file with the “append” flag, you’d get a lot of asterisks strewn through the file. (I7 tries to write an asterisk at the beginning of the file to mark it as fully written, but it wasn’t properly positioned at the beginning.)
This turns out to be a mistake in my comments in the Glk spec, which everybody copied into their code – including me – except for CocoaGlk (the Mac library). I’ve posted fixed versions of the CheapGlk and GlkTerm libraries; other libraries (and the associated Glulxe and Git interpreters) will be updated soon.
Sorry for the hassle. I don’t think anybody’s used this I7 feature much; at least, Erik Temple’s post last week was the first report of the problem! But if you run into it, now you’ll know what it is.