Density units change during calculation

I have an issue with the dimensions of density, variable roe, changing after I define it.

I defined roe := 2.62x10^-12xkg/m^3. 

When I used in a calculation I did not get the result I was expecting, especially with the wrong units.

So, I displayed the value of roe right below my definition and the units changed;

I got: roe = (2.62x10^-21)x1/kg^2

Where did this come from?

I ended up defining roe in terms of slugs/ft^3 and the equations were correct then on.

I entered: roe := (5.084x10^-15)xslug/ft^3

When I then displayed the value of roe in English units I got: roe = (2.62x10^-12)xkg/m^3

just like it should be.  The following equations are solved correctly.

Question: what gives?  I attached the actual Mathcad file.