Premature senility

When I scroll down to reply to a post (usually a post that has had no responses) I find the cursor refuses to change to 'Insert Text' mode (from the arrow thingy to the "I").

The video link shows me refreshing the screen then trying to place the cursor at the top left of the Reply window.
Note how it will change if I move to the right of the window - but it immediately reverts when I move it to the left.

After 45 to 60 seconds it changes of it's own accord.

http://www.mediafire.com/watch/c72oy0g36v3dfk3/1(2).avi

Edit:same using FF or IE.
Same on two PC's.
So it aint the senility factor.