I meant to say. I have upgraded apt to version 0.8.10.3 (as installed in squeeze), but the problem still occurs:
qqqqqqq Up-to-date Important packages in section admin qqqqqqq
*** Imp admin apt 0.8.10.3 0.8.10.3 Advanced front-end for dp
*** Imp admin apt-utils 0.8.10.3 0.8.10.3 APT utility programs