EN
We study the problem of whether $𝓟_{w}(ⁿE)$, the space of n-homogeneous polynomials which are weakly continuous on bounded sets, is an M-ideal in the space 𝓟(ⁿE) of continuous n-homogeneous polynomials. We obtain conditions that ensure this fact and present some examples. We prove that if $𝓟_{w}(ⁿE)$ is an M-ideal in 𝓟(ⁿE), then $𝓟_{w}(ⁿE)$ coincides with $𝓟_{w0}(ⁿE)$ (n-homogeneous polynomials that are weakly continuous on bounded sets at 0). We introduce a polynomial version of property (M) and derive that if $𝓟_{w}(ⁿE) = 𝓟_{w0}(ⁿE)$ and 𝒦(E) is an M-ideal in 𝓛(E), then $𝓟_{w}(ⁿE)$ is an M-ideal in 𝓟(ⁿE). We also show that if $𝓟_{w}(ⁿE)$ is an M-ideal in 𝓟(ⁿE), then the set of n-homogeneous polynomials whose Aron-Berner extension does not attain its norm is nowhere dense in 𝓟(ⁿE). Finally, we discuss an analogous M-ideal problem for block diagonal polynomials.