virtualbox installs other backports packages and

[Anil Duggirala <anilduggirala@fastmail.fm>]

virtualbox from backports is installing various packages from backports
(qt4 libraries). I dont know exactly how, but this package is messing up
my system, for example now, upon trying to install calibre I get:
calibre : Depends: python-qt4 (>= 4.9.3-4) but it is not going to be
installed
E: Unable to correct problems, you have held broken packages

I have reinstalled my whole system twice due to this problem, can
someone tell me anything about the virtualbox package in backports??