Bug#642261: me too

[Paolo Greppi <paolo.greppi@libpf.com>]

This happens here as well, same theme (Oxygen), same LibreOffice version 
(3.4.3); see attached screenshot.

First workaround: drag using the middle mouse button (if you have one) 
and you'll be able to move the otherwise non-reacting horizontal scroll-bar.

Second workaround: switch to any style other than Oxygen; also works if 
you switch to any style other than Oxygen, resize LibreOffice windows to 
force redraw of the scrollbars, then switch back to Oxygen. If stays OK 
until you resize again.

Attachment: calc.png
Description: PNG image