Robert it is for sure a paste problem but i don't understand who changes the url.

I just copy a clean URL with no html. Not sure from where you see i pasted html code, i didn't. I assure you i did not. Ever.

I paste a clean url img and somehow it is converted into what you say.

After you paste it, click on {;} button in editor toolbar and check your pasted HTML.

Robert.

I copy the url in to my text editor and shows ok. Same as the source url.

I paste in here and it is converted. Simple as that. Now if the editor here or your script does what it does, i have no idea. All i know is that it doesn't work right.

Now i see the same happens in WP editor in blog posts also. Maybe WP changed something ?

wpForo doesn't have extra functions in editor. All comes from WordPress/TinyMCE. It seems they doesn't allow image links in paste process.