Raining underground, and inside at seemingly random areas during a rainstorm

Was mining underground when I heard rain, which confused me because rain isn't usually very audible at Y=12. Then, as I came across one of my tunnels, it was actually raining from the roof, from a few random blocks. I found these weird little rain patches all throughout my tunnels. There's some screenshots inclosed below. Probably the strangest bug in the snapshot so far lol.