Just few pictures, it happens obviously in underwater tunnel with glass under certain view angles (try slowly moving left-right or up-down) turning to non-transperent. You can test it yourself on Extreme Survival Minetest (lookup coordinates).
System:
MT 0.4.13 64bit (msvc)
ATI Radeon HD 6870
Catalyst 15.7.1
Windows 7 (64 bit)
Config:
anisotropic_filter = true
bilinear_filter = false
connected_glass = true
enable_bumpmapping = true
enable_parallax_occlusion = true
enable_waving_leaves = true
enable_waving_plants = true
enable_waving_water = true
fsaa = 0
generate_normalmaps = true
leaves_style = fancy
maintab_LAST = multiplayer
menu_last_game = minetest
mip_map = true
name = Fixer
server_dedicated = false
trilinear_filter = false
language = en
cinematic = false
creative_mode = true
fixed_map_seed =
free_move = false
mainmenu_last_selected_world = 2
mg_name = v7
public_serverlist = true
fps_max = 120
viewing_range_nodes_min = 70
wanted_fps = 75
address = 23.28.75.103
remote_port = 30000
enable_minimap = true
minimap_shape_round = false
sound_volume = 0.5
fast_move = false
noclip = true
selected_world_path = D:\Games\Minetest\minetest-stable\bin\..\worlds\CarboWorld
world_config_selected_mod = 1
munin.enabled = true
active_block_range = 1
enable_damage = true
server_announce = false
wieldview_node_tiles = false
wieldview_update_time = 2

