I'm using KDE 4.5.3 on Gentoo amd64, and as I was just browsing the web as usual I opened up Dolphin and I noticed that the widget style I had changed. My other windows were still using Oxygen, but this one wasn't. I went to System Settings -> Application Appearance, and on the Style tab Oxygen was missing. I thought something in my ~/.kde4 might have gone bad so I checked another user account and Oxygen was still missing.

Why did the Oxygen Widget Style dissapear and how can I get it back?

First, make sure the Oxygen style plugin is still available. Check in $KDEDIR/lib/kde4/plugins/styles for "oxygen.so".

If present, try removing ~/.config/Trolltech.conf and running "kbuildsycoca4 --noincremental"

Finally, try running an application as follows: "<app> -style oxygen" and see what error messages are output. It will likely crash. You may need to rebuild Qt/KDE to fix this.

All I have in /usr/lib64/kde4/plugins/styles is qtcurve.so
oxygen.so is gone for some reason.

You need to rebuild kdebase in this case then, to fix this.

I couldn't figure out which package oxygen.so belonged to in Gentoo, but after going to Gentoo's IRC I found out it's in kde-base/kstyles.

Originally I thought it'd be in kde-base/kdebase-desktoptheme

What's wrong with The oxygen style?!

It disappears for me quite often. Now it happened again after an update of the kde packages on a kubuntu installation but it must be the 4th-5th time as far as I remember during the last year (in different computers combined).

The fix is so simple and everything is back to normal when I remove the file " ~/.config/Trolltech.conf" but do you know why this keeps on happening?

Do you have an unusual setup, such as packages installed from an experimental repository?
Alternatively, do you have multiple versions of Oxygen installed at the same time (as one would with KDE development)?

Nothing exotic.
KDE SC 4.10 installed from the Kubuntu ppa backports.

fyi google'ing brings up similar issues in diff distro's with the same fix and there is a bug report https://bugs.kde.org/show_bug.cgi?id=314662

Thanks for the info!

The bug is in a "RESOLVED FIXED" state?

strange usually (sometimes) there is a commit noted or a statement as to when fixed, you may wish to post your experience and ask that it be reopened

Can you verify all packages are up to date?
Also, do you have any proprietary Qt applications, such as Opera installed?

All packages are up to date. I ran the apt-get update && apt-get dist-upgrade many times since I posted in the forums this morning.

No I don't have Opera (by the way I thought that Opera is not using QT anymore: http://www.omgubuntu.co.uk/2009/12/oper ... han-chrome) and the only proprietary software I have in this laptop is Google Chrome and Oracle Java 7.

Hm, I'm mystified then. Does the Trolltech.conf file show any other changes other than the disappearance of the Oxygen style? Some other directory could be masking it possibly.

Unfortunately this time I just removed Trolltech.conf to make it work since I knew the solution so I can't tell much about the "defective" file right now.
I will post in this thread again when (and if) it will happen again. But if I consider that this has happened to me quite a few times, I expect it to happen again.