IPPM left/right labels get misplaced on massive IPPMs

[caiw]

E.g.

[caiw]

WTF this doesn't happen consistently. Sometimes running the same plotting script locates the labels correctly. Bonkers!

[caiw]

Oh, I think it's this issue: https://stackoverflow.com/questions/27892824/matplotlib-axis-text-coordinates-inconsistency
Will try a simple fix.

That didn't work, and actually I think the inconsistency is due to the fact that blocks are currently ordered randomly (#547)

[caiw]

This is therefore blocked by #547, else it's too difficult to test