Hi Stuart,
Yeah, sounds like the InfoPath designer didn't clean up correctly.
I would create a new view and copy the old view into it (using Ctrl-A/Ctrl-C, switch view and then Ctrl-V). If that solves your problem, you can set the new view as default and delete the old view.
If not, you may want to spelunk the manifest.xsf. Go to file->publish->export source files. Create a folder and export the files to it. Close InfoPath. Navigate to folder. Right click manifest.xsf and choose edit with notepad. Search for the offending fragment. See if you can figure it out. Be very careful deleting sections since if you mess up the designer won't even open the form template. When you're done, save out. Now, right click the manifest.xsf and choose design. Save the template as an XSN.
Let us know if you need some paid support. We do offer it. ;)