- Start a new question
- Tick the community wiki box
- Fill in question and answer
- Make up a new tag
- Submit the question
The page comes back complaining about not being able to create the tag due to <150 rep on this site.
What you probably wont notice (not least because of the big question preview separating the two) is that the community wiki box has become unticked.
(It'd also be helpful if the question submit wasn't necessary to find this out - the tag lookup is capable of telling if it's a new tag, so it should have warned before the submit also.)
This occurred on the main webapps site, and I've just reproduced it here.