Oil loses viscosity – thickness, to most people – as it warms up so oil pressure on tick over falls. This is particularly so if the idle speed is set a little on the low side, while the setting at which the oil pressure switch operates varies within limits.
If you’ve got the oil nice and hot, the engine speed falls below normal on braking (which can happen) and the switch is set a little high, flickering will occur without any real problems. And if the light is merely flickering, that is enough on tick over; you’re still getting at least 5psi, which is enough off load at those rpm.
But if you’re really worried, change the switch!