Well there is definitely something going on there I just tried it on my SID install here and it installs fine:
Code:
HappyTux:/home/stephen# apt-get -s install kbear
Reading Package Lists... Done
Building Dependency Tree... Done
The following NEW packages will be installed:
   kbear (2.1.1-1)
0 upgraded, 1 newly installed, 0 to remove and 17 not upgraded.
Inst kbear (2.1.1-1 Debian:testing)
Conf kbear (2.1.1-1 Debian:testing)
HappyTux:/home/stephen# apt-get install kbear
Reading Package Lists... Done
Building Dependency Tree... Done
The following NEW packages will be installed:
   kbear (2.1.1-1)
0 upgraded, 1 newly installed, 0 to remove and 17 not upgraded.
Need to get 2547kB of archives.
After unpacking 9019kB of additional disk space will be used.
Get:1 http://ftp2.de.debian.org testing/main kbear 2.1.1-1 [2547kB]
Fetched 2547kB in 17s (145kB/s)
Reading package fields... Done
Reading package status... Done
Retrieving bug reports... Done
Reading changelogs... Done
Selecting previously deselected package kbear.
(Reading database ... 86090 files and directories currently installed.)
Unpacking kbear (from .../kbear_2.1.1-1_i386.deb) ...
Setting up kbear (2.1.1-1) ...

localepurge: Disk space freed in /usr/share/locale: 848K
Try apt-get --purge remove kbear then install with the kbear/unstable maybe even post the output of the simulated install so we can see what it is trying to do during install.