Update pygraphviz to latest version from 1.3. Note there was no 1.4, only a release candidate.
Apologies DataDrake, as I'd built the original package and uploaded it here I just used the version on my machine for the update, I didn't realise from the documentation that I had to clone the Solus version rather than the source. Hopefully this is okay now (I'm still fairly new to this!).