Yepper that the same message we all get. Ever since moving to Beta build 22623.1020 that message still pops up but the hide checkbox remains checked so the taskbar will still hide itself. Most times it also caused the bottom of any open windows to draw away from the bottom of the screen by the same distance as the height of the taskbar.
That forces me to resize those windows so they skirt the bottom of the screen. Sometimes it doesn't affect the window size but most times it does. You'd think that MS would've fixed this years ago.