Starting a mission in online multiplayer at an Apocalypse PLUS threat level yields a confirmation/"USER Starting Mission" box with a threat level of
Current result: Apocalypse VII
Expected result: the Apocalypse PLUS threat level

This is a visual bug - The selected threat level of the mission is not altered.

For example:
Start an online game and enter camp
Invite 1 or more online friends
Open the map and select a mission
Select Apocalypse PLUS 9
Select Start Mission
Observe the "USER Starting Mission" dialogue box