Rated 3 out of 5 stars
I'm having a problem with this in Thunderbird v3.0.4.
The text is inserted, but it is overwriting 3 (or so) lines of text preceding the selected "Autotext" entry.
If I remember to enter several blank lines before the Autotext entry, it comes out OK. But if I forget, the previous text is wiped out, and cannot be "UNDOne".