On several occasions I have experienced that changes done to item types looks like it has been successfully saved, and on the first time i open the item type I can fill in information.
But after I save content to the new item type for the first time, and then open it next time the content and new item type fields are gone.
I can make a video of the problem if anyone is interested, its a bit hard to explain.
Im using DW 9.2.6