Using 11.3 on widnows 10, this input

ClearAll[w, x, y, a, b, lambda, mu];

pde = D[w[x, y], x] + (a*Exp[lambda*x]*y^2 + mu*y - 
        a*b^2*Exp[(lambda + 2 mu)*x])*D[w[x, y], y] == 0;

sol = DSolve[pde, w[x, y], {x, y}]

gives

When changing 2 mu to just mu the kernel error goes away

ClearAll[w, x, y, a, b, lambda, mu];
pde = D[w[x, y], x] + (a*Exp[lambda*x]*y^2 + mu*y - 
       a*b^2*Exp[(lambda + mu)*x])*D[w[x, y], y] == 0;

sol = DSolve[pde, w[x, y], {x, y}]

why does DSolve generate this kernel error on first input above but not the second? Is this a bug?