usually if land textures overlap water textures on map_T
then you usually get a burned,black looking spots
and or random trees on your water etc.
similar to the auto trees you see in the pics above
which again is a map_t thing and the tree textures rgb value is overlying the water
I am not sure why the land pops out at different angles
Water can in fact be at any elevation on a map in IL-2
Examine Zuti's Slovenia map for an example of water at different elevations
Water in IL-2 Maps...
only need to be at 0 elevations for ships to work on it

I will download and look at this map to see what's up
maybe I can help out once I look at the files and at the map in Game

I have the map,but will download again quick to be sure there the same files or update etc.
PS:
I re-downloaded this map
I do not get any glitches with water drying up into land
The water on rivers stays as water no matter what angle or altitude I look at it
Not really sure why it would be happening as I can't reproduce the bug
Double Pss:
Is this only in FMB ?
Do the rivers do this flying in a .mis file ?
I know ATI cards sometimes do not work that well on Perfect settings in the FMB
and they run better in excellent settings in the FMB
Although they work fine on perfect settings in game flying missions
Try running excellent settings in FMB to see what the rivers do for you
and perfect settings in game flying a mission over Serbia