With version 15 the integral does not give 0, it returns unevaluated. What looks to me like a bug is this result by IntegrateChangeVariables:
IntegrateChangeVariables[
Inactive[Integrate][Sqrt[1 - x], {x, 0, 1}],
y, y == Sqrt[1 - x]]
% // Activate
The output is zero, while it should be 2/3.