Hi TG, sorry you've experienced problems.
We have only recently introduced the attachments facility on the Tech boards here, and following Rik's lead, I have just increased the maximum attachment size to 512Kb, with a maximum of 2 attachments per post.
Hey Rik, however it happened it definitely didn't do that in IE. I went back and it was an empty "post reply" page. In another SM forum if I go back it does the same thing; loses your post. But in that forum if the image doesn't work it just tells you and leaves you with your preview post ready to edit your attachments. This one just reported the failure with no preview, and said go back to edit, and when I went back it was gone.
As for 'losing' the text from the text input box, I believe this not to be an SMF issue, as such, but something that seems to occur if you navigate away from the page you're typing on, before actually making the post. It has happened occasionally to me, and whilst I agree, it's most annoying, I don't think it's actually a fault with the forum, but a symptom of user navigation. A 'failed' attachment should return you to the post, as Rik said above, and you can then copy the text to re-submit the post. I also believe that this may be dependant, to a degree, on the way your browser handles cookies. If my memory serves me correctly, did you not have a problem with cookies, and with staying logged in to the forum, some while back? I wonder if that could be related?
by the way , another problem I've found with Simple Machines in IE, is when I fill up the text area, as I type anything below the visible the scroll constantly jumps up and down from the visible text area to where you are typing. It's almost impossible to read or edit when this happens. I'm not sure if the same thing happens in Firefox, but it definitely seems to be a problem with SM.
I think that is definitely a browser issue, as it doesn't happen in SeaMonkey or Firefox.