extJs: The Non-editable grid row

Back in extJs: getClientRects() error I mentioned that for some reason the bottom row of one of my grids was non-editable. The grid concerned only had two rows and sorting it at least once, on any column, resolved the issue and made both rows editable. I've since confirmed that adding another row to the grid doesn't fix it, the last row is still non-editable.

Various things I've tried doing to solve this:

• Calling fireevent on the headermousedown event (which was never going to work, stupid me!)
• Calling fireevent on the headerclick event
• Calling fireevent on the headerdblclick event

Nothing seems to work. More frustratingly, nothing in Google seems to provide me with the answer either. Aaaaaaargh!!!