Reply to myself (and OP) -
Since I was only partway through the process, I stopped, deleted my return, uninstalled Turbo Tax, restarted the computer and reinstalled. Starting a brand-new return and it's working properly now. Instead of a $30k refund it's now showing a $26k tax due (I haven't entered deductions or estimated taxes yet).
Before doing all that, I had double-checked every 1099 and everything looked correct. There is definitely a bug in Turbo Tax this year!
