Step 0: type something.

Step 1: after that text, click on the "Mention" Icon and select a user

Step 2: Insert

Step 3: Mention system loads, cursor is before the mention

Step 4: the cursor jumps before the template

Apparently, this problem is not happening when you only use the shortcut and your keyboard:

1. in the textfield type @
2. select a user using up and down arrows
3. hit Enter
4. the template is inserted, the cursor is at the right position, you can continue to type