Actually, this had nothing to do with mdadm. The scripts were waiting for the resume swap partition, which was autodetected by mkinitramfs, but can not be found anymore because it was encrypted with a random key.
As a workaround, I added the following script to /etc/initramfs-tools/hooks:
#! /bin/sh
test -f ${DESTDIR}/conf/conf.d/resume && rm ${DESTDIR}/conf/conf.d/resume
return 0
But what is the correct way to disable resume partition autodetection?
