File upload content-type side effect in IE?

[jackysee]

I have a form that have an optional file input. I let the form plugin to handle the form enctype for me. The form would be re-used to submit multiple records. I found that in IE the plugin would have side-effect on form's enctype. e.g. Submission as follow:

1. submit with no file --> content-Type submitted as application/x-www-form-urlencoded
2. submit with file --> content-Type submitted as multipart/form-data
3. submit with no file again --> content-Type still multipart/form-data

Looking into the source code shows that the plugin have set form's enctype at 2nd submit, so the 3rd submit is also detected as multipart.