I had this bug for some months but a kernel upgrade seems to fix this. The problem only happened to me after aptitude invoked dpkg for (re,un)installing packages. I use it over a ssh session in a headless server.
Recently I changed my kernel from Knoppix's 2.6.19 (*) to a custom 2.6.22.6from kernel.org, now aptitude works fine. (*) yep, I had to install Knoppix 5.1.1 and then upgrade and de-Knoppix-ize the system because the hda=remap63 is not recognized in a pure-Debian 4.0installation and full formatting wasn't an option :(
