Steps to reproduce:
1. create a folder, rename it to something containing '&', e.g. "a&b"
2. add this folder to bookmarks bar
3. watch Nautilus printing stdout/stderr

Nautilus generates this output multiple times per second:
~~~~~
(nautilus:5461): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Fehler in Zeile 1: Entität endete nicht mit einem Semikolon; wahrscheinlich haben Sie ein &-Zeichen benutzt, ohne eine Entität beginnen zu wollen - umschreiben Sie das »&« als &
~~~~~
(translated:) Error in line 1: Entity not terminated with semicolon; You probably used the character & without trying to start an entity – replace »&« with &

I think there is some escaping missing.

Additional info:
The same problem exists with bookmark names containing '<', e.g. "a<b"
~~~~~
Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Fehler in Zeile 1, Zeichen 30: »b<« ist kein gültiger Name: »<«
~~~~~
(translated:) Error in line 1: Character 30: »b<« is no valid name: »<«

This probably happens with other HTML/XML special characters too.