Consider merging https://chromium.googlesource.com/chromium/blink/+/3df333dde854facbf7253312181db1d399249569 Fix for pasting content into a text area when middle clicking on a link in Linux which has an event handler that focuses a textarea. When adding the unified version of middle mouse button pres in rev 129750 a bug was introduced that also pasted the text from the clipboard in a focused input field when clicking on a link with the middle mouse button, if the link focused an input field in its click event handler.
The patch is slightly wrong since it removes the GTK+ codepath, but I guess it makes sense.
(In reply to comment #1) > The patch is slightly wrong since it removes the GTK+ codepath, but I guess it makes sense. Blink only targets Chromium, so I removed the GTK+ codepath there. I wouldn't merge that part to WebKit.