Confusing treatment of immediates

[sarranz]

This code works

export
fn ok(reg u64 x) -> reg u64 {
    x = x;
    x ^= 3 |64u 0xffffffff;
    return x;
}

but this doesn't

export
fn bad(reg u64 x) -> reg u64 {
    x = x;
    x ^= 3 | 0xffffffff;
    return x;
}

because the operator is assumed to have size 256. Moreover, this works

export
fn worse(reg u64 x) -> reg u64 {
    x = x;
    x ^= 3 + 0xffffffff;
    return x;
}

which I find confusing. Is there a good reason for this?