Alternate titles for the same book are evil

Different titles for the same book (American and UK editions), are evil. This is the second time recently, I’ve accidentally ended up buying a book I already have. This time, it’s book 2 in the Obsidian Mirror/Chronoptika series, by Catherine Fisher. I already had The Box of Red Brocade and wrongly assumed that Slanted Worlds was book 3. Unfortunately, it’s still just book 2 and I could already have owned book 3. Also, apparently, it’s not a three but a four books series. How confusing. Or is it just me being stupid?