This came up a while back and I'm making a note of it here in case it is of interest for future improvements to MXPI..
I had just weaned myself off off Synaptic since MXPI had some recent improvements to display all installed packages on the system and Synaptic was no longer required for my purposes... Later I ended up needing to add and retain the nVidia CUDA Development Repository and packages from this Repo will not appear in MXPI at all so I had to reinstall Synaptic just to see the actual most up-to-date versions. While you could argue that I've added a non-standard Repo shouldn't MXPI show all packages in all enabled Repos?
If you look at refreshed MXPI and Synaptic side by side you can see they are reporting different versions of the same searched package name:
