Oberon's Bounty Doesn't Incrase Sandstone Yield

Sandstone yields are typically a quantity of three (3). Oberon's Bounty does not increase this as it does with other stone nodes (Schist, Granite, etc.), as no matter what my magick rating is, I always receive three, as if I didn't have the enchantment active in the first place. Additionally, striking a Sandstone node counts towards the charge depletion of the enchantment.

NOTE: The Astrolabe effect of +stone and +ore DOES increase the yield of Sandstone by the expected 100% value (i.e., I get six/6 regardless of Oberon's Bounty), so I think the nodes themselves are not seen as eligible by Oberon's Bounty.