I'm using OSX Mavericks to play this game, and one of its features is that i have multiple "desktops" which i can switch between, which I think is essentially like having multiple monitors. Generally, when an application enters fullscreen mode, that application is treated as its own desktop, so i can switch to other desktops and view other windows while it is still in fullscreen. When spiral knights enters fullscreen though, i completely lose the ability to switch desktops, so i can't do anything else with my computer until SK exits full screen mode.

I talked to a friend about this issue, and they told me that they are using a windows machine with multiple monitors and have a similar issue, where SK causes all extra monitors to stop functioning while it is in fullscreen.

I asked another friend who is using windows with multiple monitors, and they said that SK's fullscreen does not do anything unusual.