I was more pointing it out as something that might be related and might point in the right direction, than its exactly the same problem.
It does seem to be a very similar problem, though. I consistently have typing lag, but as @elextr said, there is a big lag for me with non-current lines as well - clicking on another line, or scrolling, it takes about a second for the line highlight to move to the new line. In addition, my lag is not always reproducible and doesn't happen for every letter or scroll, similar to what you're describing. I will try running Geany in F11 fullscreen to see if that affects it.