1. Yes, I'm using ConvertUnits (50px = 1 meter).
2. I added a DebugView implementation (like in "Farseer Physics Engine 3.1 SimpleSamples Silverlight") and i can see all the data:
Bodies: 3 (floor, straight square, rotated square)
Fixtures: 3 (one for each body)
Contacts: I can see that for a moment the engine is recognizing the contact between the problematic square (the rotated one) and the floor, but then it goes into the floor and (and the contact count is decreased by 1).
What did you mean by "see how your fixtures are aligned" ? How does DebugView can help me do that?