Incorrect evaiuation of of `∂x(f(x+1))` and `∫x(f(x+1))`

[c3d]

trafficstars

With f′ defined as '∂x(f(x))', we end up with x on the stack above the expression. This is not true for just an expression.

[c3d]

Same problem with the primitive command ∫

[c3d]

If we have f defined as 'x^2+sin(x)', then '∂x(f(x))' evaluates as '2*x+COS x' (which is correct) but then leaves x on the stack.

If we evaluate ∂'x(f(2*x+1)), then the stack contains '2*x+COS x' at level 1 and '2*x+1' at level 2.