Hello Jeff,
It sounds like you have a relatively old version of 2.6. How long ago did you download it?
There was a change in 2.6 that probably would cause this issue, but we identified it as problematic and remedied the issue on Jan. 25 of this year. It sounds like your build is a bit older than that.
If it will not be too much trouble for you, I would suggest getting the latest 2.6 installer and upgrading your system to that. Aside from that, the only sensible workaround I can think of is to have the form close after every submit.