Richard, you asked if

lstCastNav.RowSource = "CastFnames"

is triggering a listbox Click event.

Have you tested for this by setting a breakpoint and running the code?
If it does, you'll see it happen as you step through the code in the
debugger. I can't count the number of times I've found that Excel is
behaving differently from what I want because it's doing exactly what I
told it to do.

On the other hand, Excel is a big, complicated mass of code that runs
within Windows (which is itself a big, complicated mass of code), and
some things that really should work just don't for some reason. I've
had several occasions where code didn't work and no one could figure
out why. That's why "workaround" is in our vocabulary. :)