System stability issue with `login`.

[DrPitre]

Summary

There is an issue with system stability after using the login command that appears to be related to F$Chain. I'm not certain if this is related to the fix that was implemented earlier.

Steps to reproduce

1. Boot OS-9 Level 1 on a CoCo 2.
2. At the shell prompt, type login [ENTER]
3. Press [ENTER] at the username prompt, and you'll be presented with a shell.
4. At the shell prompt, type ex [ENTER]
5. You'll be at the shell prompt again. Type procs [ENTER]

The screen output of the procs command is garbled.

[DrPitre]

I confirmed this also causes instability on the Foenix.

[DrPitre]

A workaround is to type link shell after booting into NitrOS-9. This increases the shell's link count by 1 and prevents it from being removed from memory.

[jfed6000]

I just tried this with level 1 on a coco2:
login then procs. Shows 2 shells. mdir -e shows shell with a use count of 2. login again, procs: shows users 0-4 and 3 shells. mdir -e shows use with a count of 3. Type ex. procs works and shows 2 shells, but mdir -e shows use with a count of 1. Type ex again and procs is corrupted.