I am having the exact same issue. Whenver I add form fileds the tag structure gets scrambled.
Have you found any work-arounds or fixes?
Nope. No answer and nothing from Adobe.
I know something is going really really wrong, too: We have a product called CommonLook. It's an enterprise-level PDF accessibility remediation tool. It works well in fixing most structural problems in PDF through a relatively easy to use interface--you just drag textruns and elements around. It also has some tools that automate cleanup for accessibility.
I have no problem using this tool 99% of the time, but when I use it on forms I have made in Acrobat, the CommonLook plugin hangs when I try to save the PDF. It identifies a "structural error" in the PDF and crashes, leaving the PDF unchanged.
You can change the PDF in Acrobat by spending time moving around and creating new elements and deleting extra textruns and such, but, wow, what a royal pain in the *** that is!
Since no one is from Adobe is responding, I'm going to file a bug report.
Thanks, Ken. I'll file a report, too.