Sounds like you have some noise set in the details section of the fur attribute (lenght attribute).
Set noise to 0 and then start painting. Check the sampling of the fur feedback, not very low, not very high, (32 x 32, or 64 x 64, try the best setting for you).
Then you can add noise to make the fur look natural. Of course, the areas with 0 lenght value will have fur again. Apply a Baldness map to neutralize them.
Cheers