  We show that in 3-dimensional ideal magnetohydrodynamics there exist
infinitely many bounded solutions that are compactly supported in space-time
and have non-trivial velocity and magnetic fields. The solutions violate
conservation of total energy and cross helicity, but preserve magnetic
helicity. For the 2-dimensional case we show that, in contrast, no nontrivial
compactly supported solutions exist in the energy space.
