Puzzling results from CAS

[KeithB]

I just saw this on the HP Prime forum, but it did not get an answer.

Trying to find the roots of this polynomial:
f(x) = x^4 - 3x^3 - 2.75x² + 12x - 5
which are 2.5, -2, 2, and 0.5.

Both proot() and zeros() return: 2.5, 2, -2 and 0.

Graphing it makes it very clear that the root is at 0.5 and nowhere near 0.

BTW, how do you enter the coefficients in proot()? I tried entering only the coefficients and got really weird results.