Using the latest 8.5.4 [8915], although I noticed it in the previous version, too.
Sometimes when I add an attribute to a template, it doesn't "stick," meaning when I go to notes based on that template or even create a new note from the template, the attribute isn't shown in the attributes pane. When I go back to the template item, the attribute is now gone from the template as well.
The attribute still exists, however, and I can add it manually to items without having to change its definition.
There doesn't seem to be a particular set of conditions that cause it; sometimes it works and sometimes it doesn't.