I know this is a bit old, but I had the same problem last night. After repeatedly deleting the user cache as recommended elsewhere, without any luck, I realised that the problem was being caused by something in my code.
The form that I was using to submit the data contained checkboxes which I was using to collect the response as an array. (Using php)
By that I mean that the name of the checkbox element ended with square brackets. In my case, the name was 'conditions[]' for example.
The insert record behaviour worked fine if I removed this checkboxes.
In the end, I hard coded the insert command, without using the behaviour, which was inconvenient, but worked just fine.
I just thought it might be useful for anyone else that finds the same issue.
Hope this helps
