The Wrist item Renowned Explorer’s Lucky Bangle (edit: as well as the Shoulder item Renowned Explorer’s Mantle) (from the new RaF set) is invisible, and hence a “lookalike” of the Hidden Bracers. You can search for “Bangle”, and it shows the Hidden Bracers, but on right-click, you can only select the Hidden Bracers.
However, it can happen that, when selecting that entry or a set that had the Hidden Bracers saved, it tries to transmog the Bangle instead (have noticed no pattern across multiple characters yet) which, unlike the Hidden Bracers, costs [Base Item Vendor Value] to transmog.
It’s not much gold, even in the long run, but this is quite irritating.
Edit: If you have the same issue and clicking Hidden Bracers only selects the Bangle, I’ve found a workaround.
While in the Transmog window, enter this command:
/run C_Transmog.SetPending( TransmogUtil.CreateTransmogLocation(INVSLOT_WRIST,0,0), 104604 )
to select the Hidden Bracers.
For the shoulder slot, use:
/run C_Transmog.SetPending( TransmogUtil.CreateTransmogLocation(INVSLOT_SHOULDER,0,0), 77343 )
Edit2: It’s been brought to my attention that this also affects the Feet slot on Vulpera characters if you have unlocked the Heritage Armor, so here’s the command to select the Hidden Boots:
/run C_Transmog.SetPending( TransmogUtil.CreateTransmogLocation(INVSLOT_FEET,0,0), 104603 )
Edit3: well, I first thought it wasn’t change at all, but it seems to be partially fixed in 9.0 - selecting the entry still selects the Renowned items, but you can select the Hidden item via right-click.
I’ve updated the commands above for the new format of C_Transmog.SetPending.