Pillars surrounding Celestial Prism break Etherium generation if capped w. moonstone

[ZTagre]

I have tried repeatedly to "cap" the four quartz pillars surrounding the Celestial Prism with the "best" material - moonstone blocks, and this "breaks" the pillar's ability to generate light etherium; however, other types of caps (eg. blocks of diamond) work as expected. (1.5.0-18, MC v.1.10.2...)

[TheIcyOne]

Moonstone should prevent generation during the day, are you testing at night?