If I increase the number of large icons from 10 to 17 (the point where it actually shows up) it does show the "Run..." button, however there is now a noticeable inch gap between the "Run..." and "Shut Down" button. My monitor's resolution is at 1920x1080 with my item size set at "Smaller - 100% (default)" and my Start8 is operating in the bottom left-hand corner (where Windows use to default the Start Menu / taskbar). As I mentioned before, the issue seemed to not exist with the current Start8 settings on previous versions (+incl. Beta).
Start8 with Show user picture and Run... (my name edited out)...

Start8 without Show user picture and with Run... (my name edited out)...

Start8 with User Picture and Run... with Large Icons set to 17 instead of 10 (my name edited out)...
