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.