### bool returns true to an incorrect function call?

This happened to me by mistake.

```
sage: var('x1,t1,x2,t2,u,c',domain=RR);assume(u>0);assume(c>u);assume(x2>x1);assume(t2>t1);
(x1, t1, x2, t2, u, c)
sage: T1 = (t1-((u*x1)/(c^2)))/sqrt(1-((u^2)/(c^2)))
sage: T2 = (t2-((u*x2)/(c^2)))/sqrt(1-((u^2)/(c^2)))
sage: dT = T2-T1
sage: bool(dT.full_simplify >= 0)
True
sage: bool(dT.full_simplify() >= 0)
False
```

When I made the incorrect function call dT.full_simplify , bool returned true. When I made the correct function call dT.full_simplify() , bool returned false. Is this a bug?

Thanks