I upgraded procps on a system in which /usr is on the root filesystem and encountered no problems at boot time.
Please consider adjusting the title of this report for the benefit of your apt-listbugs readers because critical bugs cause apt-get upgrade to prompt for user input.
Kind regards, -- Ben Caradoc-Davies <b...@transient.nz> Director Transient Software Limited <http://transient.nz/> New Zealand