> Actions that triggered the bug:
>
> M-x edit-abbrevs
>
> Enter abbrevs in fundamental or global abbreviations at bottom of the list, e.g.:
>
> "dfn" 0 "definition"
>
> C-c C-c
>
> Buffer appears committed (modified flag disappears). Close buffer, test the abbrev
> in "abbrev-mode" minor mode and nothing happens. M-x edit-abbrevs again. The
> definition I entered is no longer there. This is in the same session. Emacs was not
> closed/reopened. The definitions are not applying/temporarily saving.
I'm unable to reproduce this bug either in Emacs 26.3 or on the trunk.
`C-c C-c' in the *Abbrevs* buffer updates the abbreviation for me.
Are you able to reproduce this bug starting from "emacs -Q"?
Yes, the bug exists from there too.
Brett