Hello Santa,
you are right, aptitude uses a more agressive resolver than apt-get.
Interestingly nothing else needs to be kept back.
root@sidbox:~# LANG=C apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
libldb1
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
greetings
musca