support gems in temper weapon

Hi,
I have fun with my smith warrior and the temper weapon skills but it seems that I missunderstood how the support gems work. I thought the effect of the support gems apply to the attacks that are buffed by the temper weapon skill (e.g my default weapon attack) but that doesn't seem to be the case? At least not for rage. For example, I have a "get +5 rage each hit" in my default weapon attack and a "+5 rage each hit" on my temper weapons skill. But instead of getting 10 rage I still get only 5.
Now I am wondering if the other support gems have this issue as well like "x% more elemental damage" and so on.
If that's the case why are these support gems listed as "recommended" if their effect doesn't apply at all?
Or maybe it's just an issue with rage?