oxygen-transparent or bespin window borders not transparent

[cmost]

This one is stumping me. For some reason, the oxygen-transparent window border nor the bespin window border, both of which should be transparent if oxygen-transparent or bespin themes are selected, are not. The oxygen-transparent border is simply an opaque ugly gray while the bespin border has an ugly black line separating the border from the window. Other transparent elements of the themes work as expected (e.g., they're transparent). I noticed this occurred after some updates recently, but I'm not sure what affects transparency. I have a nvidia graphics card with the latest driver installed and configured. All Kwin desktop effects seem to be working including blur. Transparency elsewhere seems fine. Any ideas of what to check? I've already recompiled both oxygen-transparent and bespin from their latest respective sources against the most current up to date libraries. Thanks in advance.