Caja file sorting doesn't work at all for "unknown" extensions

Say you have a process that produces a "DateTimeStamp.abc" and "DateTimeStamp.def" file every minute. When you go to that folder to copy the ".abc" files somewhere, ignoring the ".def" files, you click to sort by extension, and ... caja just utterly fails to work.

Because it doesn't recognise the extensions it calls both of them "unknown" for the type, and then sorts by the filename, leaving them all in the same order and making it impossible to select all the files of one type.

"Select Items Matching..." can hack around the problem to some extent, but it's much less convenient than it should be.

It CAN'T be this broken, surely. Every file manager since the dawn of time has been capable of getting this right.
Is there a flag somewhere to make it just work properly?