Achievement Beaconator working inconsistently with glass blocks

When having built a full powered beacon you don't get the achievement [Beaconator] if there are some glass blocks in different variations above it.

What I expected to happen was...:

The achievement should be granted regardless of how many glass blocks are above it.

What actually happened was...:

I tried replicating a bug and discovered, that the achievement doesn't get triggered if there are more than 8 glassblocks directly above it. Then I tried if it would work with 8 and 9 glassblocks not directly above it.

To my surpise it didn't trigger with 8 blocks not directly above it, but instead only with 6 glassblocks.

To my further surprise while trying to replicate the effects in the same world it worked in all variations, so it might be fixed by trying multiple times.

Steps to Reproduce:
1. Build a full power beacon pyramid
2. Place 10 glass blocks vertically on top and remove the one in place of the beacon
3. Place and activate the beacon - the achievement didn't fire
4. Destroy the beacon and one or more glassblocks
5. Place the beacon again - the achievement fired