If you disable the vanilla datapack, the lava texture turns into the water texture. It doesn't matter if you place lava, then disable the datapack, or vise versa.
Tested on 1.13.1 and 1.13.2-pre2
https://gyazo.com/ae70a8128c682b3551e96311d3e5239a
How to reproduce:
1. Place lava.
2. Disable vanilla datapack.
3. If lava texture does not change right away, place water next to it.
Thank you for your report!
However, this issue is a Duplicate of MC-123029.
If you have additional information, please add it to that report.
Please search before reporting, as it's likely that one exists already.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki