OM-D Second Curtain Flash

This is my first post to DP. I've had my OM-D for about 5 months but have just started using the supplied detachable flash as well as a new Olympus FL-300R. With either flash, when I use them with the 2nd Curtain Sync setting, whether in P or M mode, I get a flash at both the beginning and end of the exposure, with the one at the beginning appearing brighter. Has anyone else had this problem with their OM-D or can shed light on what settings may cause this effect?

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Amacrine