While this isn't really the biggest issue as these coaches never run together, MK1s and MK2s can run together in real life and should be able to in game without the corridor connector stretching out.
The problem are the brakes. In game Mk1 runs vacuum type and Mk2 runs air type. So you can't use them together. Cheers
On Northern Transpennine Mk1’s & Mk2’s run together. But you are right, different Mk2’s have different brakes. Mark 2’s as standard have vacuum, Mark2a–2f have air.
