  We consider the motion of an inviscid compressible fluid under the mutual
interactions with magnetic field. We show that the initial value problem is
ill--posed in the class of weak solutions for a large class of physically
admissible data. We also consider the same problem for inviscid
heat--conductive fluid and show the same result under certain restrictions
imposed on the magnetic field. The main tool is the method of convex
integration adapted to the Euler system with `variable coefficients'.
