Thanks for the link, I didn't know about that repo.
These do appear to have the same underlying causes.
For the default/river water examples,
https://github.com/minetest/minetest/issues/3263I don't have river water, but the wiki states that it can only flow 2 nodes anyway, so most of the pics are expected behaviour(?). Although, not falling next to default water does resemble my second bug.
The last one however, is exactly the eastward flow bug.
For the lava/water columns,
https://github.com/minetest/minetest/issues/2399We can speculate a mechanism like this --
The falling liquid alerts adjacent gaps on touchdown.
The southern gap looks north, finds lava, expects lava, accepts lava.
The western gap looks north, finds none, looks east, finds lava, expects lava, accepts lava.
The northern gap looks north, finds water, expects water, rejects lava.
The eastern gap looks north, finds none, looks east, finds water, expects water, rejects lava.
This scheme fits with my second bug if we imagine the depleted flow holding an 'expectation' of its original type.
A similar story works for dysfunctional lava generators.
I have yet to think of a single characterisation that covers both bugs, and maybe they are distinct.
