The Variable List in Studio is part of the Language Resources settings which are TM-specific. The other day, I wanted to use the feature for a couple of long company names that consisted of two or three words and were frequently used in the source document. With the help of the Variable List, I could define the names as placeables and then easily insert them into the target field with the QuickPlace feature (Ctrl+, or Ctrl+Alt+Down) without having to retype them constantly. This is very similar to the Substitutions/Variable list concept in Trados 2007, except that the insertion is done differently.
However, when I was translating, I noticed that only the first word of both company names was underlined in the source segment (indicating that it is a variable) and I was able to insert only that first word into the target field with QuickPlace. After I played with the settings a while, I noticed that if I only have one TM in use, the function works as it should (i.e. the whole company name is underlined and can be inserted). As soon as I enabled another TM, it went wacky again. A few more tests later, it looked like I had nailed it down. It seems like the same variables have to be listed in all enabled TMs for this to work if the variables consist of multiple words. I contacted the SDL Support, and they verified this as well.