FormBuilder not submitting when pretty URLs turned on?

[Wishbone]

I have a site where FormBuilder won't submit when pretty URLs are turned on. When I fill out the form and click "Submit" it goes back to the same form, but all fields are cleared. As a backup, I do have it write to a text file, which happens, it just doesn't send mail, or go to the submission page.

Anyone else see this and found a workaround?

CMSMS: 1.11.10
FormBuilder: 0.7.3

[chandra]

Some relevant results with debug option in config.php?
Any output with activated php error messages?
Or hints in server logs?

[applejack]

Is inline switched on or off, try changing it and in the config file is there a page extension set to either html or / try those if blank.