Oh lordy, when I bought the supermarket on Ebay the seller said that two walls were glued together for 'stability'. Turned out to be the entire serving counter, roof, all floor sections and some of the signage. Good job they used a fairly weak glue but it's an hour of my life I'm never getting back!!
Still, it did result in me being able to have a good play around with the system X components once I had. I tried a few different set-ups for the market and it's a really inventive, but fiddly, way to allow modular play. let me guess, they don't make it anymore? It's always the way when i discover something I like!