Ok, so I witnessed this in a recent tower run, very odd interaction between a Swashbuckler's Gallant Defense, and a Pig Necromancer that got charmed via the Lotus Masque.

The Swashbuckler put up GD first. Then, the necromancer targeted a group with Mojo Blast. Part of that group was another player that had on the Mask, and the Necromancer got charmed. The next turn, he ran over to our side of the map, next to the Swashbuckler.

Once the charm wore off, he stayed put, attacking as normal. However, any attempt to target him with any normal attack, melee or ranged, simply didn't occur, as if the player or companion had not entered an action for that turn. Further, any area skill that targeted the pig was "intercepted", just like Gallant Defense was still active, but no damage was dealt. When this happened, "Guarded" showed up over the Swashbuckler.

Once Gallant Defense wore off, damage and targeting returned to normal, and we were able to proceed.

It's a very odd, specific set of interactions, but you may want to look into it.