I came here to report this bug as well. After further testing, I've discovered that it only works if you surround the source Lava block with Solid Blocks. If I put slabs around the source block or the source block just below a step, the bug does not occur.
Perhaps related, my "Super Fuel" achievement is not registering at all, despite having used non-bugged Lava as a fuel many times. Other achievements register as expected. I hope that resolving this bug also resolves the achievement issue.
Only in my Windows 10 PC Version. Not happening in Java Version.
Jacob Brookover
I came here to report this bug as well. After further testing, I've discovered that it only works if you surround the source Lava block with Solid Blocks. If I put slabs around the source block or the source block just below a step, the bug does not occur.
Perhaps related, my "Super Fuel" achievement is not registering at all, despite having used non-bugged Lava as a fuel many times. Other achievements register as expected. I hope that resolving this bug also resolves the achievement issue.
Only in my Windows 10 PC Version. Not happening in Java Version.