Both responses to my question were useful. Thanks to both responders!
The first suggestion (to delete the 1099 and clear browser cache) fixes this problem and as well as many others in TT. The issue is that things you type while "exploring" TT options that you don't ultimately stick with (like whether to split tax exempt interest into specific states) are retained by TT and can confuse things downstream, especially with State returns.
The second suggestion (to force "Multiple States" into the first option and then back out and select the second option to fill in its appropriate values) also fixes this problem and without having to re-enter then entire 1099. It's less generally-applicable to other TT misbehaviors, but it took so much less typing, I prefer it.
