aptitude: why there are so many packages on hold?

[Erik Steffl <steffl@bigfoot.com>]

  since certain time (few months) aptitude puts a huge number of
packages on hold - this time it's about 100. I can still hit '+' and
they are installed without any problems - there are no conflicts (most
of them, some packages are on hold for a reason).

  why is it happening?

  TIA

	erik