Similar to Fig. 2, but for Simulation B with an external magnetic field of 5 μG, showing the progression of the bubble evolution at 1, 2, 4.3, 4.5, 4.51 and 4.6 Myr. Unlike the non-magnetic simulation, the swept-up shell of shocked ISM is relatively thick, which prevents the formation of thin-shell instabilities. The overall-shape of the bubble is ellipsoid owing to the magnetic pressure which slows down expansion perpendicular to the field, but the evolution of temporary structures inside the bubble is similar to the non-magnetic case. A faint sign of instability can be seen along the contact discontinuity, but the instabilities do not grow over time.