I posted some photos using the XF add file feature using IE8 and it was placing the photos within the post erratically, sometimes before the text that was in the reply box, so I think the options of full image and thumbnails need some more work.
I agree, I think something is broken. I just uploaded a file to my site and when you clicked insert full size image, it used to be sized according to the size of the window. Now it gives me a scroll bar to move left to right instead of resizing the image.
I am going to test one here to see if it's my forums, or Beta 6 causing it.
The original issue sounds like it's related to focus, though I'll have to do some testing. If you aren't focused on the text area when the button is pressed, it doesn't know where to put your cursor (that's down to the browser). But I'll still have to confirm.