I tend to forget a lot of things, so I don't remember if this bug is already known and was reported and discussed here.
Anyway, Mathcads symbolics gives a wrong solution for a simple equation:
but if we use "fully", we get the correct solution, as any value from -1 down is a valid solution:
And also if we replace the square and square root by an absolute value, Mathcads answer is OK:
EDIT: Just noticed:
MuPad knows that
and so we get at least no wrong results if we simplify before we solve
Nevertheless, returning a numerical wrong result in the first place is an absolute no-go in my opinion.
Regards
Werner