I reckon this has to do with the fact that yellow vendors are not necessarily friendly targets.
Try to increase your reputation with their faction to at least friendly and you'll see that it works.
The HB API seems to make differences here.
It's not a ZR2 issue in that case but an issue of the HB API function being used.
However, if you tag a green vendor first and go to the repair vendor tab, you can copy the vendor line and add it into you profile manually,
adjusted with the ID and coordinates of the yellow vendor.
IDs can be found here
Wowhead: The one thing on which Ninjas and Pirates agree. (search for the vendor's name and copy the ID from the URL).
Coordinates can be taken from the HB Developer Tool.