Problem: Mentioning or tagging people with accounts on many instances

[weex]

If you want to add someone to a toot or reply, you'd typically type @ then their name. Then the web UI will provide suggestions by searching its account database, but in cases where the individual has accounts on more than once instance these suggestions may not include the preferred account. This means, the entire @username@example.com address must be typed out which is inconvenient and error-prone.

[aschrijver]

Think common terminology is Mentions (and both "mentioning" and "tagging" are sometimes used).

The username dialog has 4 entries, while there can be more accounts that match the name you type after '@'. Also the suggestions are different than what you find when typing the name in the search bar. For example typing '@DeadSuperHero' and the first suggestion is the account '@sean', which happens to be the active account. This is not found via the search bar when searching on '@DeadSuperHero'. In the case of Sean Tilley there are 6 matching accounts.

Other than the account not appearing in the dialog is the problem deciding which account is the currently active one. Often this is the one on the top of the dialog list. But not if a person actively uses one or more alt accounts (e.g. one for personal use, another for work or programming). This is more annoying, because to find out you have to use the search bar, and click the results one by one until you find the right account to choose. In the web UI you can do a search without losing the status text you already typed. I don't know if that is also possible in other popular clients.