Since the bug MC-35790 was fixed, I got interested and looked at the barrier block, and as you can see in the screenshot, the barrier block shows a water flowing animation at the sides, unlike the glass. May be WAI.
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This issue duplicates MC-91224

This is not a duplicate of MC-91224 since barrier blocks are not transparent blocks.

Yes it is, a barrier is a solid, transparent block, like glass, if it isn't transparent, it won't be see trough, this is a duplicate of MC-91224, there is no argument that doesn't make it a duplicate

Well, that would mean it won't be fixed sigh

in my opinion, I think it's better that it won't get fixed, else you will barely even see there's water behind the barrier, and you can't see the barrier neighter, barriers are supposed to act kinda like air, but not let enities pass, so it also renders water as it should

Barriers are supposed to be completely invisible blocks. What is the issue here?

OK, OK! Sorry!

Dupe of MC-91224, but FYI: glass isn't solid, it's a full block. Barriers are solid and full.

Honestly, I don't think this deserves to be a duplicate. Someone please reopen this. The whole purpose of barrier blocks is to be 100% invisible but at the same time solid. What this bug does is ruin the whole purpose of the block; Now from being invisible, you can clearly see it underwater. Yes, barrier blocks are also transparent and all transparent blocks have that thing underwater, but since barrier blocks are a special type of block, I think it deserves a special behavior. And don't get me started on how this sounds like a suggestion, because Minecraft Wiki literally says this so:
"A barrier is an invisible block which appears transparent, but has mixed properties."
Can confirm for MC 1.12.1.

Please make this bug invalid. This is no longer considered a bug from a while ago.

Going to leave it open since MC-91224 was recently reviewed and reopened by Mojang.