On more than 1 computer, for quite some time (years it seems) Opera will intermittently lock up when I click on a 'Download <something/PDF/thing>' link on a webpage. 'Download this Awesome PDF!' > click > download indicator in the top right shows 'full' (nothing has yet come up on screen) and everything is frozen in the window.
No 'Save As' or 'Download' or anything comes up and when you try to click on anything else in the window (or any tab) you just get the windows sound that means 'you can't do that right now!'
I've attempted to clean up Opera but it doesn't seem to matter on either computer. I've also tried killing random Opera tabs through Task Manager but I eventually hit on one that closes down All open windows and you have to restart Opera and try again.