What's up with the U key (back) function?

I use the U key on my laptop to go up/back a level in the SDMB.
Today it appears to not work most of the time.. Eg, I’m in MPSIMS reading a
post.. I hit U to go back up to MPSIMS, and it goes to the post in MPSIMS
I was reading before. Hitting U again goes back to the main categories page.
Very annoying.