Lava and Water bucket bug

Hello. I'm here to report a bug I just found on Minecraft: Java Edition. So I'm playing on my survival world, and about to create a cobblestone generator. I grab a bucket of water and lava in my hands that used to be milk buckets (I needed to drink it for the materials), and when I got back to create the generator, they turned back into milk buckets! I was so mad. Please fix this!