Weird behaviour of updating flavored package via pkg_add -u

Hi!

Today is my upgrade day, so I traditionally run `pkg_add -u`, but this
time I get a really weird output:
Ambiguous: choose package for irssi-1.2.0
a 0: <None>
1: irssi-1.2.1p0
2: irssi-1.2.1p0-socks
Your choice:

All other packages, including mupdf, upgraded with expeted output:
mupdf-1.14.0p2->1.15.0: ok