Author: Vid the Kid
[Added to the original trac issue at 2.03am, Thursday, 13th August 2009]

Ref shields are drawn at the middle point of a way. Since a bridge is a very short way, Mapnik tries to render a shield on it. If there are no nearby conflicting labels, then there the shield goes. At low zooms, this often completely covers the bridge.

One possible solution would be to add a filter to the ShieldSymbolizer to exclude the case when there's a bridge=yes or bridge=true tag. One better solution, if possible, would be to add a filter based on the way's length instead. (Really it's all short ways that have this problem, whether they're bridges or not. Long bridges could still use a ref shield.)

I think this should maybe be categorized as an enhancement, since the current behavior isn't really wrong, just a little ugly, and some tweaks to osm.xml might make it better. Anyway, I agree that this enhancement would be a good and useful change.

Author: ALE!
[Added to the original trac issue at 8.01am, Friday, 20th November 2009]

This also applies to short tunnels. E.g.: http://www.openstreetmap.org/?lat=45.8426897227764&lon=8.66153955459595&zoom=17

Author: math1985
[Added to the original trac issue at 11.43pm, Sunday, 30th March 2014]

This issue has been resolved in the meanwhile.