The bug https://sourceforge.net/tracker/index.php?func=detail&aid=3515955&group_id=4933&atid=104933 is due to a bug in sign:
(%i6) e : ((sqrt(abs(sin(x)))-cos(atan2(0,sin(x))/2)*sqrt(sin(x)))/(sqrt(sin(x))*sqrt(abs(sin(x)))))$
Maxima says sign(e) is zero:
(%i7) sign(e);
(%o7) zero
but, for example, e doesn't vanish at 4:
(%i8) subst(x=4,e);
(%o8) 1/sqrt(sin(4))
I think e vanishes when sin(x) > 0. This bug may be due to the (crazy?) persistent way sign works.
Compare
(%i9) map('sign, [sqrt(x),x]);
(%o9) [pz,pz]
to
(%i10) map('sign, [x, sqrt(x)]);
(%o10) [pnz,pz]
Expanding e allows Maxima to conclude that sign(e) is pnz
(%i24) sign(expand(e));
(%o24) pnz
Don't panic: I'm not suggesting that a fix for this bug is to insert calls to expand.
--Barton