XRAY - Model racing cars

Hey all, just checked my car with regards to front AND rear downstops and making sure equal distances off the ground for both the left and right side of the car. After doing this (it was done exact) I put on tires/rims (Hudy/Sorex combo). This is when I encountered problems. I then lifted the car from its centre point to check that both wheels lift off the ground at the same time. The left wheel lifted about 3mm of the ground before the right wheel, this happened on both the front and rear of the car. So I swapped wheelsets and problem was solved! Both left and right wheels on the front and rear of the car lifted off the ground at the same time. So my question is A) how common is it to have uneven wheels and B) has anyone else had this problem? Hudy/Sorex wheelset were brand new and glued 100% correctly.