GtkFrame has no frame border drawn?

[Richard Shann <richard rshann plus com>]

I've recently noticed that the GtkFrames in my application have lost the
line drawn around the frame - the text is present but not the line.
I see that in the documentation

file:///usr/share/doc/libgtk-3-doc/gtk3/ch03.html

the widget is illustrated without any line too. I am building and
running against GTK version 3.4.2 on 64-bit Debian Wheezy.

The same application built for Windows using GTK 3.6.5 *does* show a
line around frames, albeit rather indistinct...

Is this a known bug?

Richard Shann