unvanquished map compilation issue

When q3map2 compiles metro.map against "/opt/unvanquished/pkg" and "~/.unvanquished/pkg",
and only that (not against "/opt/ioquake3/baseq3" or "/opt/tremulous/base"),
it complains about:

WARNING: Couldn't find image for shader textures/common/caulk
WARNING: Couldn't find image for shader textures/common/clip
WARNING: Couldn't find image for shader textures/common/weapclip
WARNING: Couldn't find image for shader textures/common/hint
WARNING: Couldn't find image for shader textures/common/origin
WARNING: Couldn't find image for shader textures/common/trigger