-i5 4460 @3.2GHz
-AMD RX 580 4GB
-Windows 10 (1803)
Minecraft Java Edition, 1.13-pre5
Found on newly generated flat map, creative, solo.
When water is on a Magma Cube, bubbles are going down as expected, but when a piston replace the MagmaCube by SoulSand (and vice versa), the bubbles aren't changing their way. Manual replacement of blocks or of the touching water is required.
MC-126685 Bubble columns don't update when placing magma blocks or soul sand above them