I haven't run it down yet, but for some reason WordStar always saves to drive a: -- could be disk handling or could be some problem with the WS configuration. Try this:

../../target/debug/iz-cpm --disk-a . --disk-b ../wordstar33 --disk-c ../zork --disk-d ..
b:
ws
N        (new non document)
B:TEST.TXT     (or just TEST.TXT)
Anything        (type anything)
^KX

The file TEST.TXT will now be on A: Even stranger, it tries to read from B. So if you do a ^KS instead of ^KX the file will be saved but it will reread from B where the file is blank. The same thing happens on other drives. The save winds up on A and the reread comes from the drive you intended. So if you save to drive A it works fine. Any other drive, no.

A related problem is a side effect. If you are testing and do ^KS to save, your file goes blank (because it saves to A and rereads from B). If you now save again (say a ^KX to get out), you will write a blank file over your original file on A so now when you type the file on drive A it will be blank. Not really a bug because it would not happen if the reread were picking up the file which it would if the save had occurred on that drive.

I'll let you know if I find anything else out. This is on a clone of the repo, by the way. I have not tried it with the release version.