Something strange seems to be happening. The packages libecm1 and libecm1-dev do not upgrade by default:
# apt dist-upgrade
Not upgrading:
libecm1 libecm1-dev
Summary:
Upgrading: 0, Installing: 0, Removing: 0, Not Upgrading: 2
They are not held:
# apt-mark showhold
But they do not remove anything when installed... (I meant to run "apt -s install libecm1 libecm1-dev", but I actually installed both, as I had tested before, but forgot the "-s". Oops...

)
Why was it being held back? I was assuming it was the new solver preventing other packages to be removed, but it was not the case in this example.
Any ideas?