Why cursor movement is closing cell during edit

Hi,
I'm appreciative of any feedback on the following:

During the edit of a cell in excel 2007 (editing text) when I move my cursor or use backspace the cell closes as though I was hitting the ENTER key.

When I go back into editing the cell using F2 I don't encounter this problem.

Seems to only occur on the initial edit of the cell.

I suspect a setting.

Thanks,
Chubster