Very strange problem.
When editing big script (5-8 screens), after some large mouse selection was made and cancelled, any further mouse selections cause serious flickering (editor turns white for a moment). Very often it even causes the mouse to not leave "button pressed" state when real button is released. It's actually almost unusable for me when it's like this.
I have a copy of 1.6.8 and I've compared both versions - there is absolutely no such bug in 1.6.8. Also the editor feels much more responsive there.
I've tried to swap updated files with their old versions from 1.6.8 but ultimately failed to find which one exactly is causing this condition.
I'm not using hardware acceleration in Opera.