That's not my experience. The account details stay open for me.
For me the UX is not amazing, but ok. A bit better than LastPass, a bit worse than 1password.
https://recordit.co/QdK2FrRoYX I copy the password, go to paste it in and it loses the selected account:
https://recordit.co/jrvUFWCPkS Here, I go to add an account. I generate a new password and then I try to paste it into the text box to verify it meets the website's password rules. I then go back to hit save, confirming that it worked and it loses the entry.
Sooo frustrating.
I use Bitwarden myself and I only need the copy/paste button for stuff like email and WiFi passwords. If you're manually copying and pasting data, you're probably overlooking one of the many (sometimes not clearly indicated) features Bitwarden has.
Hope this helps!