What I expected to happen was...:
A. Lava always blows up for a given explosion strength
OR
B. Lava never blows up for a given explosion strength
What actually happened was...:
"Flowing lava" will blow up in any explosion while "still lava" will not blow up. This can be quite noticeable in survival when using multiple blocks of TNT near a lava lake.
Steps to Reproduce:
1. Dig three holes with one block of soft material between them
2. Place TNT in the center hole
3. Place lava in one of the other holes
4. Dig a hole directly next to the remaining hole so the lava has somewhere to flow to
5. Ignite the TNT
6. Place lava in the upper part of the third hole shortly before the TNT explodes
7. Wait for the TNT to explode
8. Observe that the first block of lava you placed is still there while the second one has blown up