You cannot interact with Sea Weeds at all under the light of a mushlight/glowcap

When you place a mushlight or glowcap near a sea weed (the barnacle plant) you cannot shave them at all during the night. You cannot attack them either or examine them, basically cannot interact with them in any way. This is exclusive to sea weeds as beefalo can be shaved under the light of a mushlight/glowcap.