can't boot after kernel upgrade to 2.6.27-11

[Pierre Frenkiel]

hi,
these 3 last days, Ubuntu people realeased 3 kernel versions:
   2.6.27-11.25 2.6.27-11.26 2.6.27-11.27
each time, the dpkg.log seemed perfectly normal
     upgrade linux-image-2.6.27-11-generic 2.6.27-11.26 2.6.27-11.27
     status installed linux-image-2.6.27-11-generic 2.6.27-11.27
but "dpkg-l ..." gave:
  pi  linux-image-2.6.27-11-generic 2.6.27-11.27  Linux kernel . . .

question 1: what means exactly "pi"?
   According the headers, it's for  "desired = Purge" "status = Inst", but that
   explains almost nothing...

Then, I couldn't reboot, as the modules were not actually installed
and I had to run "dpkg --reinstall install" for
   linux-restricted-modules-2.6.27-11-generic
   linux-image-2.6.27-11-generic
   linux-headers-2.6.27-11-generic
   linux-headers-2.6.27-11
to fix it.
question 2: did anybody have the same problem? (I had it on 2 computers)
question 3: has anybody an explanation?

cheers,
-- 
Pierre Frenkiel