Not a viewer issue as all, but it might appear to be. In short, in some situations, when you detach a headset from its base, the left mouse button will stop working. This may lead you to think it is a viewer issue, if you use voice only with a SL viewer. However, this is in fact a problem with ubuntu and derivatives - and possibly other distros as well.
From this thread:
Run lsusb to find your USB device vendor and product IDs:
$ lsusb ... Bus 001 Device 005: ID 1395:740a Sennheiser Communications ...
We're concerned about “1395:740a”. If you are using a different headset with the same issue, your ID will be different. Now, open up /etc/X11/xorg.conf with your favorite text editor, and add this somewhere:
Section "InputClass" Identifier "Sennheiser OfficeRunner" MatchUSBID "1395:740a" Option "Ignore" "on" EndSection
The Identifier string can be anything you want, although since we're blacklisting it, you'll never reference it. Put your USB vendor and product string above into the MatchUSBID string. Restart X and you're done.