Interesting mistake – It can be "solved very easily" – I think
(https://www.simplemachines.org/community/proxy.php?request=http%3A%2F%2Fimg339.imageshack.us%2Fimg339%2F7380%2Fdontmovebuttonbx2.th.jpg&hash=02289c1404df800e8160dae9d2e6f5fa0c68c575) (http://img339.imageshack.us/my.php?image=dontmovebuttonbx2.jpg)
Look at red field – Try to click several times – very often used when you have several attachments. Button goes below your mouse with "last" line for adding attachments – If you have like me very often chance to add more than 10 or even 20 attachments – that can be frustrating
Suggestion
Isn't better that button (more attachments) stay at same place – where clicking on it will not be so frustrating :)
PS
I am not sure is this connected to SMF in general or to Helios (by block) – theme I use – I think it is connected to whole smf forum – If I am right – than I think it can be included like improvements in next patch.