ArcGIS Server WMS URL Syntax Incorrect

Having a strange issue consuming WMS services hosted on ArcGIS Server 10.3.

When the service is cached in ESRI's compact format, the request fails with HTTP 400. In exploded format, it works perfectly. I've tracked down the issue to the CRS parameter. For example:

`http://ift.tt/1902XsR...'

will fail based on the CRS=CRS:84 parameter. If I change that to CRS=3857, it succeeds. Again, this only happens with compact format. I thought it might have something to do with the BBOX units, but the parameters for exploded are identical and it works.

The service was published as EPSG:3857. For what it's worth, the server was installed as 10.2.2 and upgraded to 10.3. I haven't tested through a fresh install of 10.3 or through an older version, but suspect it wouldn't matter. Have an open ticket with ESRI but have yet to hear back.

I've also tried editing the service's cfg with listCustomCRS and listSupportedCRS to no avail.