There seems to be a really weird problem with blending in Corel Painter.
I have used 2 brushes. They are both on the same Normal Gel layer. However only the left brush can be blended, the right brush cannot be blended. If I change the layer to reference layer, and then undo, then I can blend the other brush... what the hell is going on?
I spent a bit more time working with these brushes, and eventually noticed that the right brush is "Digital Wet". I think perhaps Corel Painter preserves some information about the paint so that it can be further diffused when needed.
Due to this diffusion preservation, it means that it's unable to work with regular blenders and can only be blended with digital wet brushes.
Good investigation, Carlosamegos...yes that makes sense that Digital Watercolor brushes are unable to be blended so they can be further diffused. If you go to Layers > Dry Digital Watercolor, or perform the shortcut of "Ctrl+Shift+L" (Cmd+Shift+L on a Mac), you can blend these brush marks, however the fringe cannot be futher adjusted.