How to reproduce: → Open Dolphin → Go to 'tags:/' → Increase the zoom-level to have icon-sizes >48x48 Result: The icon is blurry. This applies to the preview icon in the information panel (F11) as well where it is independent from the overall zoom-level of Dolphin.
Besides that, I wonder whether another icon should be used anyways, as 'mail-tagged' referers to tagged mails and might be represented in a mail-specific way in other icon sets than Oxygen, so generic 'tagged' icon might be the way to go here. Changed the bug description to reflect this and created Oxygen bug as dependency.
And another update. The icon used until now is not 'mail-tagged', but the visually identical 'feed-subscribe' (which is even more wrong from a semantical point-of-view). Should've taken a closer look at src/kioslaves/tags/{tags.protocol,kio_tags.cpp} earlier :-)
Marking as CONFIRMED.
Breeze now provides a 'tag' icon which we are now using. commit 4eb2555cd4cca1bf31604ec6edaa015a3b936562 Author: Vishesh Handa <me@vhanda.in> Date: Thu Feb 12 18:12:34 2015 +0100 tags kioslave: use the tags icon The breeze theme ships with an icon called "tag". BUG: 332209 FIXED-IN: 5.9