Since the injected material is placed in an area that is constantly mobile (your mouth), the product will definetely move around a bit...some people will observe this effect more than others...for obvious reasons...does this result in the lumpiness you feel? Personally, I don't think so. The effect of placing a dermal filler in a mobile region of the face is that the filler is not going to stick around as long...you will notice the effect fo the filler diminish more quickly than will placed, say, at the superior portion of the nasal-labial fold.
There are a couple of different tissue planes that Restylane and other fillers can be injected into...just beneath the surface of the 'red skin' of your lip, or deeper into the muscle.
Personally, I like to do a very subtle lip augmentation just by outlining the vermillion border (red skin) with Restylane or Juvederm, and then a bit of product beneath the 'wet' regions of each lip. I never use more than 1 cc for a pair of lips. The 'augmented' lip looks strange, and I avoid it by minimizing the treatment volumes to 1 cc.
The 'lumpiness' is probably more of an artifact of the injection technique, rather than the product actually moving around. Other docs may have a different opinion on this matter, but I think the lumps that you can feel relate to the way the filler was deposited.
The lumps might not be visible, but I'm sure you can feel them with your tongue, or other lip. They will subside in a few months as the product volume diminishes.
Most Kindly,
Scott Sattler MD FACS