It doesn't look like you did the @Mentions thing correctly Art.
When you type the "@" symbol and start typing the member name a box opens up with the names of the members that contain that sequence of letters. You need to select their name from the box. If you just type the "@" symbol, type their name, and keep typing the feature doesn't work. You'll know it's been done correctly when after you type everything their name and the "@" symbol is blue in color which makes it a link, like this:
@TRP