Until my PC was upgraded recently I have mostly used VS version 7. So I cannot say whether this is new. On this new machine I decided to finally switch over to this new version.
No, it does not happen with every search. I only had the feeling that it might be related to searches until I had one case where it noticed the issue directly after hitting 'y' on the 'search wrap/continue' dialog (it still is a little bit a fuzzy observation).
Yes, the Window Left Margin set to 0.0 did not help either.
Strangely, when I tried re-creating this issue just now, using a .h file, the .c file that showed the gray strip, now no longer has the gray strip!
Under tools/options/editing/bookmarks I have all switches set to OFF.
When I installed V18 on the old PC, I let it import/migrate the config from V7. Could that be the problem?
Going back to an empty config and re-applying everything would be a bit tedious.
But then, my colleague, who has I think V19, also has the problem, but he has line numbers on all the time and hence does not notice this. (Checking with my colleague's V19, not all of his editor windows have the extra space after the line numbers).