Since upgrading to 2.6.13 from 2.6.4 in stable the autocomplete has been
very buggy and bordering unusable. Here is a simple way to reproduce my
problem (I'll attach a screenshot).

1. Create a new file using the standard template
2. In one account add a transaction with description "Monthly ISA
investment"
3. In the same account add another transaction with description
"Mortgage payment"
4. Go to the description field of a new transaction, type the characters
"Mo" and GnuCash autocompletes to "Mortgage payment" and places the
cursor *after* the 't' at the end of "payment", even though it hasn't
got enough input to disabiguate this.

This is quite painful to workaround as GnuCash makes it very difficult
to go back and edit the text without it autocompleting again.

Here's two screenshots to illustrate:

http://pasteboard.co/jjkb2DHt3.png
http://pasteboard.co/jjkpLanD1.png

After playing around a bit more I noticed two other behaviours
sometimes, seemingly at random:

* As described in the first report, except that the cursor will remain
after the 'o' instead of jumping to the end of the description

* It will not auto-complete until you type the next character (either
'n' or 'r') to disambiguate - which is the correct behaviour! But this
only happened 2/10 times I tried.

This bug still exists and is EXTREMELY annoying. Strangely, it only
happens on one of my two Debian machines. Not sure how to figure out
what causes the difference.

@Nick, are you on KDE? I've had this for a while, and I suspect it's related to https://bugs.launchpad.net/ubuntu/+source/gnucash/+bug/1319523 which links to https://bugs.gnucash.org/show_bug.cgi?id=730195. It could be some issue between GNUCash's quickfill libraries (yes, they wrote their own) and KDE's implementation of whatever GTK libraries upon which it depends.

I don't get the problem on my Windows installation.