Hey, thanks for the reply (also @Shawn Blanch). The Voxel-Remesh does the trick (it almost feels like cheating :D). Blender already prevents using dyn-topo and remesh at the same time.
I tested a little bit and I found out that it happens to me when I move my mouse to quickly. If I move the mouse very slowly, then I can inflate as much as I want. But is there a way to prevent this from happening ?