Stacked Ethernet shield Heating

When I do this stacking, it heats up. I tried connecting the SPI via ports 13-10 (no stacking), it doesn't work. Also tried connecting the ICSP via male-female wires without stacking, it works, but still heats up. So I think the ICSP has a defect? or does it? Is it supposed to be like this and I'm just being paranoid?

*PS: the heat in the "pain" level when I touch it, no burning IC odor. Maybe it's because I unplug it immediately after short use?

So what exactly is it that heats up?

And is it actually functioning?

The W5100 Ethernet chip gets very hot. It is too hot to keep my finger on it, but that seems to be "normal". I have added a heatsink to it.
The newer W5200 and W5500 are better.

Perhaps a voltage regulator gets warm, but only the W5100 gets hot. If something else gets that hot, then something is wrong.
Stacking the boards has nothing to do with it.