I have noticed several times one bug in x86_64 Debian – your low panel turns half-black and you can do nothing about it ;). Usually it looks like this:
Now, if you adjust panel height it seems to fix the problem, however it can become black again in the future. Debian has this bug filed, but not fixed. I guess it is not fixed because it only happens in x86_64 builds. I never encountered this in x86.
The solution is to wait until the next release of KDE will be pushed in Debian, or to use a workaround which consist in removing the KDE cache content from /var/tmp/kdecache-USER_NAME.
Try to remove this folder for your user, i.e., assuming your are logged on as sheldon, perform the following:
1. rm -rf /var/tmp/kdecache-sheldon
2. log out
3. log in
If it resolves your problem, you can set to auto remove your cache when machine starts. In order to make this, add the following into your /etc/rc.local file before line “exit 0”:
rm -rf /var/tmp/kdecache-sheldon