It's impossible to delete the user if you use the same name you've used on other operating system that shares the same /home partition

[aleksandar-todorovic]

This is kind of hard to explain, so here's how to replicate it:

1. Install elementary, use a separate /home partition, create a user (I'll call him user 1).
2. Install some other operating system (in my case Fedora), use the same /home partition, but create a different user (I'll call him user 2).
3. Boot into elementary and create a new user, but use the name user 2.

What happens:

It's pretty much impossible to delete the user 2 after that. I logged in as user 1, went into User Accounts, unlocked the settings, clicked on - sign and everything seemed fine. However, once I clicked on the Power indicator, that user was there. When I logged out, that user was still there.

What's even more interesting is that elementary doesn't accept my password for user 2 anymore. I can't login as user 2.

When I login as user 1 and try to open /home/2 using Pantheon Files, I get the following message:

This does not belong to you.
You don't have permission to view this folder.

When I sudo into Files, I can clearly see all of the relevant data and nothing seems lost.

[Fabian Thoma (fabianthoma)]

To me this is pretty much the expected behaviour. The owner of the files in /home/2 is not the same user as the one you created on elementary OS, it is the one you created on fedora.
elementary OS also rightfully deleted the actual account of the user (on elementary OS), that is why you can't log in with him, why he shows up in the indicator is to be investigated, but it's probably something to do with the home folder, could you test for that in some way?