On a multiplayer world, I tried to break it with an axe and by hand, but the wooden irrigation channels (specifically Biomes O' Plenty's Redwood) won't break. I then went into creative, and finally broke them, but their collision models were still there, and they appeared for every other player like they weren't broken. When I relogged, they appeared in the same place for me.

Seems like a serious desync bug, thanks for reporting.

Does this only happen with BoP wood?

I tested Hellbark, Willow, and Pine (both from BoP) Irrigation Channels, and the same still occurred. They are unable to be broken. I then tested vanilla Oak and Spruce Irrigation Channels, and the same occurred. It appears none of the channels are able to be broken.

What about the latest version? Ive tested vanilla wood in my dev env and that works fine.

Confirmed by #783.