When pushing a water logged block with a piston, it removed the water from the block.
Linked issues
is duplicated by 10
MCPE-188381
End rod/Lightning rod makes water dissappear
Resolved
MCPE-134560
[Water log glitch]
Resolved
MCPE-96832
When a piston move a slab with water, the water disappear (I think with stairs is the same)
Resolved
MCPE-90995
Waterlogged stairs pushed/pulled by piston removes water
Resolved
MCPE-86254
water disappears fro waterlogged blocks when they are moved
Resolved
5 more links
As a Parity Update for v.1.16.0.51 - Beta Blocks will now lose their waterlogged state when pushed by a piston, reference here:
https://feedback.minecraft.net/hc/en-us/articles/360040975731-Minecraft-Beta-1-16-0-51-Xbox-One-Windows-10-Android-
Fixes and Changes
Parity