LMDE's apt reports wrong version of packages

Hi,

I needed to access Emacs 29.4, so I've activated the "backports" repos for Bookworm in LMDE, following this tutorial:
https://linuxcapable.com/how-to-install-backports-experimental-repository-on-debian/

Since I was used of using standard Mint & Ubuntu, and I didn't notice the final remark, saying that you need to use "-t bookworm-backports" flags to apt to specifically install/configure packages from backports, I started using "apt" the "usual way" (no flags) after configuring the additional repos.

I was very surprised to observe that apt is totally wrong about what it does!!!

# apt install emacs --update
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
emacs is already the newest version (1:29.4+1-4~bpo12+1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

$ emacs --version
emacsclient 28.2

Even when purging and reinstalling Emacs, apt reports installing version 29.4, whereas it is still version 28.2 that gets installed!!!!

Reproduce the report using the backports repository configuration, apt install emacs --update, and the reported emacs --version check. Investigate why apt's selected package version differs from the installed executable; done means identifying a reproducible cause and documenting or fixing the mismatch with a verification case.