The bamboo hopper does not float when on non-vanilla water fluids. For example, TFC's Salt Water, both minecraft:water and tfc:saltwater are tagged with #minecraft:water.

Seconding! We use IA in a TFC-based modpack as well.
A config setting to whitelist other fluids, or something similar, would be handy!

I'm a bit unsure why it's not working out of the box, since I am using the minecraft:water tag.