Invisible separators in TLB 4.4.8.1 beta

I was using the last official version (4.4) up to today, but have just updated to v.4.4.81. This appears to be working fine - and it's a really great piece of work - except that the plain separators are now invisible, and are detectable at all only as a narrow space between the particular buttons. Separators including a title do show quite a thick and prominent line, so they are working correctly - it's just the plain separators.

I'm using Win7 Home Premium with all the latest Windows updates.

This problem manifests both in the basic quick-launchbar version and in the standalone version. Any ideas about this?

Kind regards,