I purchased a set of carts for my 4900 to be able to use Piezo Flush. While I was able to get it to work (and it did an excellent job cleaning the stubborn clogged heads) I noticed that when I push the carts in there is no spring to them. For instance, when done, if I push on the carts nothing happens (they don't pop out like the Epson carts do). If you want to remove a cart, you have to first remove the cart to the right of it, so you can grab it with your fingers. I also noticed that when I first put some of the carts in they weren't recognized by the printer. After taking them in an out, the printer would recognize them. Am I doing something wrong? I didn't see anything in the instructions or FAQS on this issue, but maybe I'm missing something. Thanks for any help.