I got the following code wich is not consistent. There should be a bug in there. The priority of the parenthesis is not respected in the first case.
sage: version()
'SageMath version 9.0, Release Date: 2020-01-01'
sage: ....: Qpart(x) =5*( unit_step(x)
....: ....: * sin(x ) -
....: ....: sin(x))
sage: Qpart
x |--> 5*sin(x)*unit_step(x) - sin(x)
sage: ....:5*( unit_step(x)
....: ....: * sin(x ) -
....: ....: sin(x))
5*sin(x)*unit_step(x) - 5*sin(x)
