Christian Land

Yeah, I read his tweets regarding glass. 

Personally, I think "Mobs don't spawn on top of light-sources" (no matter if they are solid blocks or not) would make perfect sense as a "rule".

I only noticed the glowstone-thing when i was testing my AFK-gold farm (its a design where you AFK on top of the nether and use spawning-platforms that are dug into the netherrack just below the roof) and suddenly had a lot of pigmen spawn on top of random glowstone-blocks around my farm (as everything else is non-spawnable).

And I totally agree with you on not changing certain core-mechanics. At least not if there isn't a really good reason for it (for example I'm kinda OK with the village-changes as they actually try to come up with something completely new).

Mobs will also still spawn on top of glowstone.

I did a quick test (in the final release-version of 1.14) and created a glowstone-platform in the nether and both zombie-pigmen and ghasts were still spawning  on top of it.

Edit: Mobs also spawn on top of sea-lanterns.

I've got a 1.13.2 world that i converted to 1.14 pre 4 yesterday (using the Optimize-function and with the Delete Cached Data-checkbox enabled) and while lighting was OK when i converted it to pre 5 today, torches stopped working after i went to the nether and back a few times.

I then deleted this world and converted a backup of my 1.13.2 world to pre 5 - again using the optimize-function with the "Delete cached data" enabled. And again: lighting was OK for some time but after going to the nether and back a few times, torches stopped working again.

So far it seems that i can somewhat reliably reproduce the issue at my wither-skeleton-farm which is kinda special as i push skeletons into a portal to kill them in the overworld. So what I do is, I AFK for a few minutes in the nether (during this time skeletons will go through a portal every couple of seconds) and then go to the overworld myself (using a different portal). And after some time, the torches break. Sky light will be 15 and Block light will be 0 (during the night) for the torches.

I will do some additional tests tomorrow to see if i can gather some additional informations.

Edit: You can see this bug happening in the latest video by LogicalGeekBoy (https://www.youtube.com/watch?v=VHXi1dhntvI) at 16:20 -> and at 25:45 you can see that he is using the pre5-Version

Try converting the world to 1.14 pre1 using the "Optimize World" function and make sure to enable the "Erase cached data" option. This should rebuild all height- and lightmaps. After doing this, my world was back to normal.

Still happens in 19w14b but now the blocks where the torches are placed also LOOK like they are  illuminated. But the lightlevel is still 0.

Here is a screenhot:  

I just converted my 1.13.2 world (using the "Edit > Optimize" option in 19w14a) and the whole area where i logged in was set to lightlevel 0. I then went to check on one of my farms (to see if an issue i had is resolved in this snapshot) and the same had happened over there. Everything was set to lightlevel 0.

Replacing the torches fixed the light-level (but is really not an option as this would mean i have to replace hundreds of torches ans sea-lanterns in the world).

Edit: Just to see if the "Optimize"-function is bugged, i copied my 1.13.2 world and opened it without using Optimize first. Results are the same: lightlevel is set to 0. 

Mob-spawning in general has become incredibly strange. I've build a squid-farm using ilamngo's design (checkerboard of sugar-cane with columns of water (and kelp) between them) and haven't seen a single squid spawning there in the last couple of snapshots (at least since 19w11a - before that it produced more than a stack of ink per minute). I also have a creeper-farm with 2 block high-spawning platforms (with trapdoors preventing any other mobs from spawning). And again: nearly zero spawns since 19w11a (i probably see a single creeper every couple of minutes - in 1.13.2 creepers are constantly spawning there).

All spawner-farms I have are working just fine, as does my slime-farm (and apparently my witch-farm - but i only checked it very briefly).

All in all, mob-spawning seems to be pretty badly broken at the moment. Or lets say: very, very weird.