So, our skillful thomasd solved an issue I had raised.

In the Gnome desktop, when dragging an application toward the folating bar
on the left, the whole desktop environment crashes, it restarts and you
have to log on again.

The problem is a missing mouse cursor, as stated here
https://gnunet.org/bot/log/guix/2017-02-23#T1301986

And the proposed workaround works like a charm.

For reference, it is
1) "mkdir -p ~/.icons/default"
2) "ln -s /run/current-system/profile/share/icons/Adwaita/cursors/
~/.icons/default/cursors"

What could be a definitive solution to patch the Gnome package with ?