Bizarre one this: Using SharePoint 2010’s new Modal Popup functionality a link had been created from a tab control to launch the new form for the list items associated with the tab. However, every time the form was submitted, it overwrote one of the existing records in the list. Firstly, I thought I was imagining things !!! But, it turned out that this was caused by using the ID key in the query string. I changed ID to RefID all was well.
It makes sense when you know, but it took a while to figure out why this was happening.
Lesson Learned: Don’t every use ID in the query string of a NewForm.aspx
