If I have two or more tabs of the SEGA Forums and one is logged in and the other isn't, if I click on anything else other than "Post Reply" or "Post New Thread" (e.g. schanging pages) on the one that isn't, the one that is will lose the logged in satus on its next click, not mattering what I try to do. Is there any way to fix it other than logging in to all tabs (sometimes it's more than 15 >_<)?
It sounds like normal operation to me. If you're using the same browser with no special IE-addons, etc. then both of those tabs will share the same cookies.
One action executed on the first tab will likely show up on the second. If you log out and try to post a reply on a tab that appears to be logged in, you're still logged out regardless because of what's been written on the cookies stored in your browser cache.
There's no way around it other than using an IE browser tab add-on or a different browser in place of the second tab.