New hylafax version available at sourceforge (5.5.4).
Just compiled 5.5.4 using my old ebuild from #438600. Everything went fine 'til now. Will have an eye on incoming and outgoing faxes...
...successfully sent and received some faxes in the meantime - one of the sent faxes was a 17-page long tax-thing, so I can say 5.5.4 is working stable :)
*** This bug has been marked as a duplicate of bug 438600 ***