Thanks for all the information guys it's much appreciated. I'm glad I wasn't an electrician in Vienna those flats sound a nitemare. Presumably they had 2 supply transformers for the 2 different systems
Nope, I'm sure that was just messy wiring and people not thinking straight. Basically wrong wire colours in parts of the place, not much else. And fused neutrals but that was common anyway because no one bothered to remove one of the fuses when supplies were converted from 127/220 to 220/380.
As I said, the meter tails were clearly original and intended for 220/380 3ph + neutral so the circuit wired with same-colour wires must have been a mistake or ignorance. There were other fun details too - apparently PVC conduit was still expensive back then so they tried not to use too much of it. When they ran out of space (2 circuits plus 2-way switch travellers in one 13.5 mm ID pipe) they switched to 0.5 mm2 doorbell wire for travellers, switched live for the bathroom fan, etc.!
We ended up rewiring a good half of the place, leaving only what conformed to the regs. Also added a whole bunch of sockets, mostly by replacing singles with doubles.