Can anyone help me to fix this problem?
I can't normally apply the custom brush while using blob brush tool.
It's not dependent upon type of brush I use.
With simple brush tool everything is just fine.
They inherently create artwork which is constructed differently.
If you draw with the Blob Brush Tool, then apply a brush stroke, you are applying the brush stroke to the circumference of the shape. Similarly to applying a brush stroke to a rectangle... the path around the shape gets stroked.
The Blob Brush tool is meant to draw just "blobs" and not be a "live" brush path. If you want a live brush path, draw with a standard brush. The Blob Brush is really merely a Calligraphy brush that gets expended when you let go of the mouse. It is 100% possible to never use the Blob Brush tool and get exactly the same artwork via a Calligraphic brush and the normal Brush tool.