When I write {{#tag:references|<ref name="a">refff</ref>}}, it will generate the error output like:
tag.; $2
Yet, when I write <references><ref>a</ref></references>, it works properly.
For detail, please check [1] for the bad one, and [2] for the good one.
Please note that this problem makes the template {{Reflist}} on wikipedia not working properly. And the example above uses group attribute but that group attribute is not the causing reason.
Please check another bad example [3].
The example [4] has the same phenomenon like the ones above.
Interestingly, the {{#tag:}} works fine with other tag names, eg: ref. Check examples [here.
Did I miss something?
P.S.: Is here the proper place to confirm a bug?