Ah, never though it could be a player problem, but it seems that is indeed the case. Don’t know why I never tested it before (I’d usually only check to see if the first few subtitles displayed or not before burning to disc without checking overlapping timings), but when using MPC-HC, the subtitles display without turning off for a few frames when there’s overlapping timings, unlike my PS3 or Oppo BDP-80.
PC playback isn’t a very good option for me right now since I have an old Nvidia card that has tearing and judder on Blu-ray playback, but I’ll have to look into other hardware options.