OpenMPT does not crash here when changing MIDI devices. The fact that OpenMPT becomes unkillable hints at a driver issue. Are you using the latest drivers for your MIDI devices?

Also, instead of killing, please rightclick OpenMPT in the task manager and select Create Dump File. This will create a rather huge memory image of the process. Compress it with 7z or RAR and upload it somewhere where we can have a look at it (the issue tracker itself won't accept attachments of that size).

here's the dump file.
https://drive.google.com/drive/folders/1ttEXA1uZn26B4WxMXcxooxrLaoGPCDHT?usp=sharing

As suspected, the code hangs in wdmaud.drv!CMIDIInDevice::Close which is the driver trying to close the old device.

Microsoft themselves suggest that this kind of issue can also occur when unpluggin device while they're active but I think that's not related: https://support.microsoft.com/en-us/help/4460006/midi-device-app-hangs-when-former-midi-api-is-used

But the way that article is phrased makes it sound more like an advertisement for the new WinRT MIDI API (which isn't any better from what I've heard).

Either way, unfortunately there isn't really something we can do here, as the issue is in the MIDI driver. If you do something similar in a program like SendSX, you will probably have the same issue.

Issue isn't reproducible in sendSX or Ableton, will update if I find the driver/software issue.

Also, please test the following just to be sure:

• Does it also happen if you only toggle the MIDI input device rather than selecting a different one? Judging from the memory dump, it should.
• If so, does it only happen with that one specific device?
• Does it always happen or only if there is or previously was MIDI data on the wire?

Problem Solved.
OpenMPT's Roaming\OpenMPT\mptrack.ini had set the midi device to one that is no longer connected, so it was hiccuping on that. editing the config manually has fixed the problem.

It only occurs when going from digidesign mbox 2 (which hasnt had new drivers in years) and AKAI MPK61. anything else works fine. This seems to be because of the specific hardware I use.

I'm glad you could solve it. It really doesn't sound like we can do anything here, just be careful with your device selection.