Thermal broadening of the first order magnetostructural transition and enhancement in ferromagnetic exchange occurs in carbon deficient Mn3GaC0.9. We show from temperature and field-dependent magnetization measurements that this leads to inhomogeneous magnetism and causes frustration and kinetic arrest effects. The arrested state is deactivated and the system returns to its ground state when the cooling-field is removed. This causes open hysteresis loops with which we study the kinetic arrest effect in this system. (C) 2015 Published by Elsevier B.V.