OK, with the Healing Brush, works or works not in this situation it is just the same, but the Clone Tool should copy from one area to another without artefacts. I think LR4 has a problem to use the tools on the border of a image, afak (i deinstalled LR3, so i can't test it anymore) there was the same problem in LR3.
The other problem is that LR4 freezes like LR3 if you have some Healing-Spots.
I think in the Clone examplem you might be touching the edge of the
building with the source spots. Try moving them further away to the right.
Can you upload this file (with xmp)? I'd be curious to check it myself.
I noticed something similar while doing some cloning in a 32-bit tiff. The first few clones went fine, then suddenly LR started inverting the cloned area. So if the source area was green the resulting spot became orange. Really weird.
The Clone circles in Lightroom have quite a bit of feather (about a third of the radius, I think) on their edges. It might well be that the brightest highlights of the building are showing through the fethered sdges. Try using a larger radius.
Again, this is just a guess, cannot say for sure without a sample file.