Version:            (using KDE KDE 3.5.7)
Installed from:    Fedora RPMs
OS:                Linux

Re-sizing the left or right side-bar is standard.  But both side-bars have a minimum size, and the handling of this is confusing.

Reducing the size beyond the minimum does nothing, but then at some point it snaps to zero.
That's a little strange, but OK.  Though in that case it seems the "vertical tab" that switches sidebar mode should also disappear - or at least clicking the tabs should restore the sidebar.  (Though in that case a better UI is to replace the "vertical size tab" by a more normal "top tab".)

What's really confusing is that sliding the divider to restore the sidebar.  For the left sidebar nothing happens until the width reaches the minimum width, which is substantial.  There is no feedback except that the cursor changes, until it has been dragged far enough to reach the minimum width.

I suggest restoring the sidebar as soon as the divider has been dragged more than a small number of pixels, perhaps 2-5, possibly depending on some global mouse-sensitivity setting, assuming there is one.