Mushrooms

Mushrooms are growing in the same pot as my truncata in sphagnum moss. Is this bad?

Do you want the mushrooms there? If not, I would remove of them,
Kevin

Well it certainly wont help to extend the life of your growing media.
I would remove them and if you havent repotted in a long time id say now would be the time. Otherwise Id just suggest letting the plant dry out slighty more between waterings and you should be fine.
Mushroom spores are quite common but when they are fruiting it usually means thing are running too damp. Lack of air movement will also assist in the growth of Mushroom spores. So the addition of a fan would help.
FWIW

Peace

The mushrooms are the fruit of the mushroom plant. The plant itself looks like little, delicate white threads that live in rotten plant material (usually). I would guess that (since I'm led to believe that neps don't have much of a root system) that perhaps you have orchid bark in your mix? This would explain it. The bark just got old and waterlogged, and the mushrooms are feeding on it.
Could this be right?

I don't think they will hurt anything, except as they may be an indication of too much wetness or an overly degraded soil mixture.

The mushrooms are the fruiting body of fungi that live by breaking down dead wood (orchid bark) for food.  They indicate that the compost is wet and decaying.

Sounds like what Tim and Khai said don't it?

I'm batting a thousand today, huh?    

Mushrooms are fungi {not a plant} and the non fruiting body is called Mycellium.

Peace