it seems that avi and mkv are no longer supported in the iXpand drive app. they released a video playback app called topreel. you should get a coupon code to get it for free when you try to play one of those videos.
the renaming of the file seems to only happen when you copy or transfer the file using the ixpand drive app. i tested and it happens to me when i transfer a file to or from the ixpand. I opened a ticket with their support as well.
