When holding a light block, you can’t see placed light blocks, but you can adjust them. When holding a barrier, you can see placed barriers and placed light blocks. So you can interact with light blocks but not see them when holding one, and you can see them but not interact with them when holding a barrier. 

Idk if this needs this but 

Steps to reproduce:

1. Give yourself barrier and light blocks in creative
2. place one of each
3. Hold barrier, then hold light block
4. try to interact with light block holding one, then the other 

Expected results: see the light block when holding it 

Observed results: can only see light block when holding barrier, can only interact with it holding light block