I used a Funguar pet in a party today and noticed that overtime the spores on top of his shroom started disappearing! I think this is something that happens just overtime (I suppose every 20 mins that the Funguar stays alive). Two other possibilities could be that they disappear after a certain amount of damage or after using Queasyshroom. I somewhat ruled these out, though, because my pet rarely took damage and only used Queasyshroom once.