An entry from the Unofficial Oblivion Patch: Version History:
v3.0.0 (2008-06-03)
Changed the Magicka fountains found in Oblivion planes so that they work as described in the book Arcana Restored (with the book and a gold nugget in inventory, the player will have the option to recharge all their magical items from the fountain, consuming the nugget)
This old change from back in the day may be beyond the scope of Unofficial Oblivion Patch, as it's debatable if it's even a bug fix and could venture into 'unbalanced' territory. It's not justified by the book either - the book calls for "pure gold", whereas the gold nugget is gold ore.
The relevant edited scripts by the UOP which seem to include this change are OblivionMagickaFountain01SCRIPT [SCPT:00154CE8] and OblivionMagickaFountain02SCRIPT [SCPT:0001481B]. Certainly this change should be at least re-evaluated for whether it truly belongs in the UOP, and removed from it if it is found to be an inappropriate addition to the patch.