broken gaussian blur

this bug's example

Thanks for your bug. What version of Ubuntu do you use?

Ubuntu 6.06 DapperDrake

$ uname -a
Linux seven-dim4550 2.6.15-27-686 #1 SMP PREEMPT Sat Sep 16 02:13:27 UTC 2006 i686 GNU/Linux

$ gimp --help
Versione di GIMP 2.2.11
(2.2.11-1ubuntu3.1 on repo)

are you sure you are not trying to blur an indexed image (is the mode really set to RGB?).
if i try to reproduce it in edgy it does the right thing and blurs the red dot i created properly to transparent.

This is an upstream bug in GIMP's Gaussian blur plugin -- it got fixed in 2.2.13. See:
http://bugzilla.gnome.org/show_bug.cgi?id=343047

And here's the commit:
http://cvs.gnome.org/viewcvs/gimp/plug-ins/common/gauss.c?r1=1.18.2.3&r2=1.18.2.4

It'd be nice if the fix could make it into LTS's GIMP, since it makes Gaussian blur pretty much useless as-is; we've just tried to get a bunch of schoolkids doing graphical stuff using Ubuntu and got hit by this.

It's very easy to reproduce: create a new image. Fill the background red. Create a new transparent layer. Draw a sharp-edged green squiggle on it. Select all and do a 15px Gaussian blur. On 2.2.11 you get a black halo around the squiggle; on 2.2.13 you get a smooth blur.

The current gimp package is 2.2.13, marking the bug fixed. The problem seems to be a small one and only one bug has been opened about it, the patch is not likely to be backported for dapper