Operator flag images inverted

[T-EGJA1]

I've installed an instance of VRS, running under mono, on a headless Raspberry Pi 2 and after the agonisingly long wait (2 or 3 minutes) for the web page to load across the LAN, it's working surprisingly well, apart from the odd quirk that most (but not all) of the Operator Flags display inverted .... any explanation or fix would be welcome.

Capture

[agw]

What browser are you using? Have you tried a different browser?

[T-EGJA1]

Same result in both Firefox and Chrome - haven't tried any others.