As puppies grow, they do tend to go through the "uglies" where their front and rear ends grow at different rates. Most commonly, it is the rear being higher than the front.
A common conformation fault in Maltese is being high in the rear. It is usually fairly subtle but easy to tell by the dog's gait as they bounce in the rear instead of trotting like they're floating.
There are also chondrodysplastic conditions that can occur where the front leg bones don't grow at the proper rate or have curvature (grow in the wrong direction). For some affected dogs this causes no problems. Others require orthopedic surgery for their comfort and to be able to walk normally. To be sure you usually have to wait until 4-5 months and x-ray then (radiographs before then aren't great because of the open spaces you would see).