RubyMine - Turning off ability to click in middle of "empty" lines
You need to disable Settings | Editor | Virtual Space | Enable placement of caret after end of line
If you find that Allow placement of caret after end of line is already unchecked, try checking the box then exit and restart the IDE. Go back into settings and un-check again. This was the only way I could get it to work on a fresh install of PhpStorm v3.0.3 - no amount of check/uncheck would disable the behavior without this restart sequence.