Fitting Room Etiquette

During Summer Vacation I did a lot of shopping, I found that it was an activity that required a safe amount of exploring with the added perk of air conditioning upon reaching the destination. In one of the malls I decided, on a whim, to go into what appeared to be a young woman's clothing store. I found that the store was having a summer sale sale so I selected this shirt. At just 1490 Yen it was much less expensive than I had expected clothing to be.
After choosing the shirt, I wanted to try it on. While it is loose fitting I've heard that Japanese woman's clothing can be restricting for Americans because of the differences in body build. It was easy enough to locate the fitting room, but as soon as I steeped in the young, overly made up, sales clerk became alarmed and started frantically trying to tell me something in Japanese. I was carrying a large purse, so I set it outside the fitting room curtain thinking she might be afraid that I was going to steal something, but that didn't calm her down. It wasn't until she started pointing at my shoes that I realized that like homes, restaurants, hotels and probably some other kinds of places I haven't been yet, I needed to take my shoes off before entering the fitting room. After asking a co-worker about the situation, I learned that removing your shoes in a fitting room only applies to the type of fitting room with a raised step to enter it, apparently if the fitting room floor is at the same level as the rest of the store the proper etiquette is to keep your shoes on. Are fitting rooms this difficult to decipher for foreigners living in America?