OK. I've been able to reproduce this (several times).
Steps to reproduce:
1 Create a folder D:\Audio with several folders of audio files (some .mp3, some .flac)
2 Unzip a brand new MC x64 portable into a new, empty directory (C:\Temp)
3 One tab in each panel. One rooted at C:\, one rooted at D:\Audio
4 Add column "Total Length" to the D:\Audio tab
5 Browse the audio files (including select/unselect/get properties) - no problem
6 Hit Tab to move to the other panel (C:\) fatal crash - no error report sent
7 In addition, most of the MC Config folder was trashed (to be expected, I guess)
See screenshots attached.
Event Log Entry:
Faulting application name: MultiCommander.exe, version: 6.4.4.2233, time stamp: 0x57a3532c
Faulting module name: MCAudioTools.dll, version: 1.2.0.0, time stamp: 0x57a3528e
Exception code: 0xc0000409
Fault offset: 0x000000000002aefb
Faulting process id: 0xd8c
Faulting application start time: 0x01d1ef3ec9ab57a0
Faulting application path: C:\Temp\MultiCommander.exe
Faulting module path: C:\Temp\Extensions\MCAudioTools\MCAudioTools.dll
Report Id: 082bbcf8-5b32-11e6-a8f0-c86000593d93
If any more info is needed, please ask.
Alan