Bard Meep Inconsistency: Runglaive vs Lich Bane

When I build Bard, I build him AP + Movement speed, to increase harass and Meep collection rate.

As support, I'll get a Lich Bane at some point, for the movement speed and AP and proc effect. A Meep-enhanced autoattack will proc Lich Bane, adding some harass at a longer reliable range than Bard's Q.

Of late I've been playing some fun normals, and taking Bard as a jungle. Since I build him AP as a support, I figured I'd try to mimic my build as much as possible, and Runeglaive is fairly similar to Lich Bane. However, an important difference is that Bard's Meeps will not proc Runeglaive.

Curious, I checked the LoLWiki, and both items utilize the "Spellblade" sheen for its on-hit proc effect: the Runeglaive should not be operating any differently from Lich Bane in that regard.

I went in-game, bought a Runeglaive, and confirmed that it does not proc on Meeps. I then bought a Lich Bane (on top of the Runeglaive) to see if I might get the Lich proc on Meeps, and the Runeglaive otherwise. I did not- I only got the Runeglaive proc. I then sold Runeglaive, and Lich Bane still would not proc on Meeps. However, if I do NOT buy Runeglaive, Lich Bane WILL proc on Meeps.

This is rather inconsistent, and I'm pretty sure one of the two items must be bugged.