No clue if this is a duplicate, I looked quite a bit of distance back on the issues, couldn't find what I'm looking for to ensure this isn't duplicate, but anyway, water and lava sometimes form in unloaded chunks. I am even able to use them as if it were a regular water/lava block, swimming at least.
Addition: Also in unloaded chunks (includes end/nether) something I'm calling Ghost rain. Rain appearing in unloaded chunks and, sometimes, when it lags like crazy.
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Please do not mark unreleased versions as affected.
You don't have access to them yet.
I can edit this bug, since I do not remember seeing anything regarding rain in the posted bugs.