Confusing derivative(sqrt(1-sinx)) result Bug? [SOLVED]

[parisse]

sqrt(1-sin(x)) is auto-simplified to sqrt(2)*abs(sin(-pi/4+x/2)), because it's much better not to deal with "false" sqrt, for example if you want to integrate sqrt(1-sin(x)).
The derivative is sqrt(2)*cos(x/2-pi/4)*abs(sin(x/2-pi/4))/(2*sin(x/2-pi/4)), it looks complicated but it is not: it's the product of a cos by a sign. If you make assumptions on x like
assume(x>0 && x<pi/2), you will not get absolute values, and the derivative is simpler -sqrt(2)*cos(x/2-pi/4)/2