The first part is because of the focus being on that Control, so you can use /did -f to put the focus somewhere that the focus won't show, such as any text or hidden control. Note that your choice of dummy control affects what happens when you press <tab>
The other one sounds like you've got a text control instead of using the text label that's part of the check control. If you've defined 2 controls with overlapping x y w h territories, then checking the box will write its text territory on top of the other control, so just shrink your 'w' or 'h' dimension.
