A lot of difficulty repositioning image attachments within post

If i add two attachments and accidently dont position the image correctly and I try and drag it the image either dissapears completely OR worse creates a littleplaceholder icon beside the image that displays nothing.

In FF it is bad, in chrome it has a nervous breakdown. 5.5.5 was OK in this regard, 5.5.6 give me grief.

Any help appreciated