Full particle simulations are presented that suggest that the strength of an ambient guide magnetic field controls whether magnetic reconnection, once it is established, remains steady or becomes bursty. Specifically during anti-parallel (component) reconnection the electron current layers that form near the magnetic x-line are short (long) and therefore stable (unstable) to the formation of secondary magnetic islands. The implications for understanding magnetic reconnection and the formation of Flux Transfer Events at the magnetopause are discussed.