Hi Brunhilda!
No, it is the change last night for the new "live"_templates!
Therefore the "starting" underscore is now an important "wikidot-language" switch , used to detect categories / templates connected for this "living" usage of tenmplates:
Template pages would be a type of a "special page" (name starts with an underscore) within categories. Examples of template definition pages would be:
_template
category:_template
bugs:_template
proposals:_template
That is the reason , why "over night" all categories ( and pages ) starting with underscores are working different…
If you want , you can now build "real" templates, which defines the layout of your pages ( in one category connected to this template) on a "living" status - means youo change teh templazte and all pages of this category using this template are changed too.