For Luke and the confused (;->) perhaps this will help. I'm using Firefox with SWF disabled, never mind which browser, the point is there is no SWF. If I were to simply post with an attachment only the invalid image number appears. If I then click on edit and again add the image it appears with the invalid number to the left. If I delete the number in edit and add the image, of course it appears without the invalid number.
Here's the reason why now none of my image attachments have a number to the left. Because first I post without an image, THEN click on edit and add the image, no invalid number appears, only the image. Please bear in mind all is done without SWF.