System Information
OSX 10.9.1

Blender Version
I noticed the issue using build 54ebaad and confirmed it for the official 2.69.0 r60991 release as well.

Short description of error

Create a plane, go to Sculpt, activate Dynamic then set the Inflate/Deflate brush to 1.0.
Draw out a few strokes, and you should now expect to see messy blobs of geometry built up on the backside of the mesh.
For me this has worked every time I tried to do it. I reset to factory defaults for both builds and it still happens.

One quick test showed that the tumors that form can end up having an absurdly high poly count.
On an area that only had about 5000 triangles, the extra blobs that were formed made up about 35000 triangles.

I tried to attach a .blend file but I received an error message that the file size limit was exceeded. (.blend ~7.5MB)