Depending how the valve is plumbed, even a blown piston seal will let a double acting cylinder stay extended as the pressure will still act on the rod area alone as it leaks around the piston.
The side effect of this is after you pick up a big load, the leakage will let the pressure go very high while holding the load and you will blow hoses as the relief valve is isolated when holding.
Scored spool will just let the oil escape. My Kubota's curl spool has been leaky from new, common problem on the cheap husco valve. Simply poor tolerances.