Moving the cursor down the font list farther causes the dialogue box to fade out (mouse-over problem):
Here it's beginning to fade and you cannot select from the list:
Thanks for reporting this! It has been reported to development.
I take it you have discovered that you can undock the text box or leave it docked but use the minus (-) sign to roll it up and it won't fade.
Thanks again,
I was trying out to see if I liked it docked or not when the problem presented itself. On my 27" monitor, I find it better to have it float closer to the center for a lot less mouse travel.
Since the font list can be scrolled using the mouse wheel, the Text Box can still be used in the vertical docked position that has the fading problem.