I tried to report this to COFH team here, but they turn me down, so I am trying it here.
When connecting Cryo-stabilized flux duct to Elite Universal Cable or Ultimate Universal cable energy gets lost. I tested it with these mods by simply creating loop from one energy storage to another, in this case Ultimate Energy Cube. Here is picture of my testing loop.

This isn't a bug, you can easily set the conversion rates within the Mekanism configuration file yourself.

Or it's just the default conversion rates inside Mekanisms configuration file is a little off.

IMHO, it's not about energy conversion.

When I connect Elite/Ultimate (only these!) Univesal Cable (Mekanism) to Cryo-stabilized Fluxduct:



And energy gets lost, although has nowhere to go.

Energy Conversion on server: 1EU = 10J = 4RF (default)

Only Cryo-stabilized fluxduct does that and energy keeps losing. If it was just conversion, energy would be same just in different units.

the mekanism cables have storage within the cable, which the cryo-stabalized ones lack

But it's only for Elite or Ultimate cables, Basic and Advanced works fine.

the size of that storage also scales with its rank, and the basic may be small enough that your not noticing it

This has been fixed, thanks!