Perhaps a misconception about the OMD Weatherproofing

Actually Olympus are reasonably clear. The E-M5 manual states "Splash resistance ... Equivalent to IEC Standard publication 529 IPX1 (under OLYMPUS test conditions)".

It's a bit harder to find out what IPX-1 actually means, as the standard doesn't seem to be published online. One source http://www.cvgstrategy.com/International_IEC_60529.html  describes it as "Protected against falling water Equivalent to 3-5mm rainfall per minute for a duration of 10 minutes." Another source suggested the same duration but 1mm per minute. Either way, that is pretty heavy rain.

The odd part is that IPX-1 applies to equipment fixed in position. If it can be tilted in any direction by up to 15 degrees, the standard would be IPX-2. In practice I'm sure that the camera can be tilted, or even turned upside down, but it would seem that Olympus don't actually test that.