Steps to reproduce:
Place water on the ground;
Set RandomTickSpeed to 4096 to make it easier to notice;
The grass will decay;
Set time to midnight.
Expected results:
The grass stays dead, and other water blocks placed above grass during night time should also decay the grass underneath.
Observed results:
The grass grows again during night time.
Relates to MCPE-46035 and those other reports relating to grass turning into dirt when there is a block above them.