compacted downloaded files are stuck on "Loading folder..."

When I download a tar.gz in Firefox and then double click it (or it automatically opens in dolphin because of the application settings in Firefox) it opens a new dolphin window but never displays the contents (as it used to do before upgrading to natty).

It just says "Loading folder..." and the blue bar bounces from left to right and right to left forever. Clicking the up arrow and the tar.gz "manually" opens the folder as before

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: dolphin 4:4.6.5-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-11.50-generic 2.6.38.8
Uname: Linux 2.6.38-11-generic x86_64
Architecture: amd64
Date: Wed Oct 26 16:46:40 2011
ProcEnviron:
 LANGUAGE=
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: kdebase
UpgradeStatus: Upgraded to natty on 2011-10-20 (6 days ago)