Was Playing a single player world, came back though the nether to my base. and started to dig in spawn area chunks. To get a "Saving World" dialog, stating "java.lang.IllegalStateException: [LibMultiPart] We've gotten out of sync! (Expected to be in the middle of drawing block outlines when we're not!)".

I've attached a gist link to the crash-report https://gist.github.com/Cheeseborgers/c6ab28971194407da046360df15aa0f4

I think this should start working if you manually update LibMultiPart to 0.5.0?

Haven't recreated it in a survival world/copy since the update.