[Sway] "Ghost" lines in Stacked mode

People,

I am really loving Sway but there are glitches / artifacts / odd things happening which I would like to debug - this one is where, in stacked mode, a workspace accumulates grey, non-functional lines at the top of the screen. In this specific case they were all labelled Vim Browser started from a Kitty terminal - I exited all instances of vimb in all workspaces but these grey lines persisted. I have seen it for other apps as well and they don't disappear until I exit Sway (of course) . .

See here:

http://pricom.com.au/2021-10-19_00-54-25_SwayGhosts.png

Anyone have an idea of what is going on?

Thanks,

Phil.