This Devuan/Ascii box shows unread mail numbers in KMail Favorites
but only when the numbers are non-zero.  All accounts here are IMAP.

$ kmail -v
Qt: 3.5.0
TDE: R14.0.5
KMail: 1.9.10 (enterprise35 0.20100827.1168748)

(I don't know why previous posters have a space between enterprise
and 35 while we do not.)

--Mike