The bug

Bamboo has cullface specified for the top and bottom faces, like many other blocks do. This works fine against solid blocks, for example grass blocks they may grow on, however it does not affect other bamboo blocks which constitute the same bamboo plant.

I originally noticed this on a Sodium instance, however can confirm it affects vanilla as well.

How to reproduce

1. Enter Spectator mode
2. Fly underneath bamboo growing on a solid block
   1. Note that the bottom face of the bamboo is culled as expected, but subsequent bamboo is not, despite these faces being completely culled
3. Compare this behaviour to cactus, where all such faces are culled as one would expect

Expected results

All internal faces of the bamboo plant would be culled due to not being visible normally

Actual results

Bamboo is only culled against solid blocks - bamboo against other bamboo blocks is still always rendered.