How to reproduce:
1. Edit the first post of a topic that does not have a poll
2. Look at the "Poll creation" tab below, "Options per user" is set to 1
3. Click preview
4. Look at the "Poll creation" tab below, "Options per user" is now 0
5. Now you can't submit the form if you have an HTML5 browser that enforces the "min" attribute of the "poll_max_options" input, which is set to 1
In short: everytime I edit a first post, I have to set "Options per user" back to 1 or I can't submit it.