Odd startup behaviour

Since upgrading to Tahoe and Sitely 6, I have noticed a very odd behaviour. It not deteremental as much as irksome. Everything else seems to work fine, but when I open the program up and get the start screen, as soon as you click anywhere on it, apart from the three buttons, top-left, the screen just jumps to somewhere else on my screen, or across to another screen. It was handy to be able to open up recent sites. Not a huge issue, as I can just go file-open recent, but marginally annoying. Anyone else notice this or found a fix?

Thanks.