My German is almost non-existent. The "besser" part corresponds to the English "better", and I believe the "-ung" ending makes the word what we would call a gerund. So I can think of trying to fix something but making it worse as "schlimm-bettering"
So what's "schlimm"?
Babel Fish says schlimmbesserung is "bad improvement", and schlimm is "badly". I didn't think it would be that simple. "Bad-bettering", yeah, I can remember that.
As much fun as some German words (such as schadenfreude or fliedermaus) are, I am really diggin' Martha's neologism. Most people I know remember the Cola Wars and New Coke, so the word would convey so much more meaning. A "bad fix" may only suggest that a problem has not been corrected, but New Coke equals "What the blank were you people thinking? Change it back! Quick!"
By the way, here's the term from an 1897 book theology.
The reader will please remember that an "emendated" text is not really an "unfaulted," "bettered," "corrected," and therefore "truly correct" text, but a text or a reading which somebody has in innocent ignorance changed, supposedly for the better, but actually for the worse. A colloquial German word, " Ver-schlimmbesserung" "badbettering," would be the appropriate term for such "emendation."