Not so magic mushrooms

[for]

According to the patch notes you can mistake them, i.e. it looks like waxing, but is waning. I have not confirmed this personally though.
The chances to mistake them are low with high proficiencies. I'm not sure how low exactly. Since getting posioned by mushrooms is just a bit annoying, nothing else, avoiding toadstools entirely creates more problems than it solves. You would have to spend much more time foraging for your mushroom pies.

[MagicManICT]

With enough skill, you should see all waning mushrooms, but I don't know what that is. At first, they all look like waxing toadstools, and you will likely get some in there you didn't identify until you reach that lofty value.

[Rydersowl]

Thanks. That makes sense. Either way I've got some work to do but this has been helpful.