A recent paper arXiv:1312.4890 on multi-symplectic magnetohydrodynamics (MHD)
using Clebsch variables in an Eulerian action principle with constraints is
further extended. We relate a class of symplecticity conservation laws to a
vorticity conservation law, and provide a corrected form of the
Poincar\'e-Cartan differential form formulation of the system. We also correct
some typographical errors (omissions) in arXiv:1312.4890. We show that the
vorticity-symplecticity conservation law, that arises as a compatibility
condition on the system, expressed in terms of the Clebsch variables is
equivalent to taking the curl of the conservation form of the MHD momentum
equation. We use the Cartan-Poincar\'e form to obtain a class of differential
forms that represent the system using Cartan's geometric theory of partial
differential equations.Comment: 12 page