buglist: bug 7266: integration failure for 1/(sin(x)^4+1)

f:=1/(sin(x)^4+1)
a:=integrate(f,x)
b:=differentiate(a,x,1)
draw(b,x=0..4)
draw(f,x=0..4)

reported by Yanyang Xiao <xyy82148@sjtu.edu.cn> 30 Nov 2014