Bracketing gets lost when substituting an expression variable into the expected answer for a mathematical expression part

[christianp]

An example.

There's a variable d = expression("a*b*c*d"), and a mathematical expression part whose answer is x/({d}). The bracketing is lost, so the displayed answer is (x/a)b*c*d.

If you define the whole expression as a variable and just use that, the display is better: x/(a*b*c*d).

[christianp]

This was the same problem as #1011 (and I even gave it pretty much the same name!)