Coin Magic Taint

I wrote here recently about coinage and treasure hoards in RPGs. Well here's something a little more lighthearted about money...

Magic leakage is a subject that has been long known about, but little discussed as it only happens very slowly, weakly, and only affects very small objects. Its effects are rarely even observable. However when large piles of coins and magic items are placed together for centuries at a time, as in, for example, a dragon's hoard, this leakage may result in coin magic taint.

Coin magic taint, the enchantment of coins through long contact with magic items, can exhibit in many ways. The most common is an attraction between affected coins and sources of magic (most commonly the same magic items that affected the coins, but if these cannot be found then any magical source will suffice). This can get players into a lot of trouble if they pay for goods using tainted coins - the coins will often creep out at night-time and attempt to roll themselves back to the players so they can once more bask in the magical aura of the players' possessions.

The opposite is also the case: in the unlikely event that players get hold of magically tainted coins, perhaps in payment for selling their treasures, they may find these coins gradually escaping from their possession and making their way back to their preferred location.

Other magical properties can be absorbed by coins: perhaps if they have been in contact with a cloak of invisibility, they will be observed to fade in and out of visibility. If tainted by a magical weapon, they may conceivably used as irregular but deadly ammunition for a sling.

What other weird behaviour have people observed from these magically tainted coins?