I found a similar bug already as issue MCPE-125648 (https://bugs.mojang.com/browse/MCPE-125648), which is already closed without any solution.

The issue exists when having installed the launcher using the debian package with version 928. The package was upgraded from version 2.2.1867, where switching accounts is working properly. After the upgrade, I also tried to delete ~/.minecraft but the issue remained.

When having configured multiple accounts properly and tested with 2.2.1867, I try to select a different account from the drop down on the top left of the window. No matter which of the accounts I select, it directly jumps back to the already selected one.

When I start the launcher through a command prompt, there are no error messages / exceptions / ...

The only error I see occurs earlier: "sh: 1: orca: not found"

Switching through Settings -> Accounts -> <activate> is working.