The present work explores nonlinear rheological behavior of a strongly viscoelastic paste made of nano-sized polybutadiene particles. Apart from conventional rheometric measurements, particle-tracking velocimetric observations are carried out to determine the macroscopic state of deformation during startup shear and after step strain. Despite its highly nonlinear rheological characteristics, the system shows no sign of inhomogeneous response to large shear deformations in sharp contrast to well-entangled polymeric liquids made of linear chains. Apparently strongly nonlinear rheological behavior can occur in absence of inhomogeneous macroscopic deformation.