When .tigrc contains

set reference-format = hide:tag

tags are hidden in main view but in diff view they are prefixed with hide:
It can be reproduced with tig's own repository:

tig show 529182c

See Refs: field:

$ tig -v
tig version 2.5.4-22-g15aab28
ncursesw version 6.1.20181013
readline version 7.0