Version: (using KDE KDE 3.5.8) Turn on the "size" column in folders pane. Wait for all sizes. Create folder "a". Delete folder "a". Voila -- most of the sizes are "-".
Cannot reproduce on 4.2.2 (Kubuntu) the size information remains for all folders in the pane as expected. Can someone re-test on 3.5.x to confirm? Thanks.
Here using: Qt: 4.5.0 + qt-copy-patches-936035 KDE: 4.2.68 (KDE 4.2.68 (KDE 4.3 >= 20090327)) kdelibs svn rev. 949044 kdepimlibs svn rev.949046 kmail svn rev. 949046 on ArchLinux i686 - Kernel 2.6.28.8 I can't reproduce this neither.
So lets close