#635698 is fixed and independent of this autoremove problem, and #635628 is filed against ecryptfs-utils which cannot "force itself" to stay installed. Therefore, I opened a new bug report to deal with this issue, agains lxdm, which appears to be a suitable candidate package for the necessary Depends: line.
There is information in bug #635698 and bug #653628 which is relevant to this issue.
#635698 is fixed and independent of this autoremove problem, and #635628 is filed against ecryptfs-utils which cannot "force itself" to stay installed. Therefore, I opened a new bug report to deal with this issue, agains lxdm, which appears to be a suitable candidate package for the necessary Depends: line.