I still use this technique and it seems to be working fine for me for LR2 through till the latest LR4 RC.
How exactly are you defining this tagset? Im using a line in Info.lua:
LrMetadataTagsetFactory = "MetadataTagsetNone.lua",
and MetadataTagsetNone.lua essentially contains the following line:
My MetadataTagsetNone does contain a couple of lines of debugging code but nothing important.
I expect you have done somthing similar. Maybe its worth a retest?
Thanks Matt - My bad: I had the name wrong. (I must be slipping...)
Np. Glad it was easily resolvable because I'd hate to have that trick break
(Apologies for the brevity - sent from my Android)