Minecraft: 1.7.10
Forge: 10.13.0.1160
Via MC Launcher
Description: UI elements are rendered translucent, invisible or black depending on the items in the hotbar.
Details in the video.
Video (4'58"): http://www.twitch.tv/ezerarch/b/544385553?t=1m30s
The bug not only affects vanilla UI elements, e.g. XP bar and counter, but also UI elements of other mods, e.g. NEI buttons.
The bug to occur depends on the right-most item present in the hotbar: if it's enchanted with any durability loss, it will affect the transparency; if the item is a sprite (non-3D model) and not stacked, it will affect partially the visibility of the XP bar overlay, renders black or invisible.
I removed all mods (entire folder) and resource packs. MCPatcher was removed, bug still present.
No log was generated.
(Off-topic: The attachment system is available but if I use it the forum returns "An error has occurred...")
Post edited with more relevant details.
EDIT: this might be related to: http://www.minecraftforge.net/forum/index.php/topic,16014.0.html