Does anyone know of this problem where pressing Alt + Enter together no longer works as they previous do?

In the past, pressing the two together while in MS Doc while create a new line (not paragraph), now, doing the same will cause it to do an immediate copy-and-paste of the whole content! For example, if I have a 3 paragraph work, it will duplicate and end up with 5 paragraphs (the last character of the third paragraph will be right next to the first character of the new duplicate without any spacing or new line).

EDIT: I switch I could swear, but I couldn't, anyway, it started working again. Mod, if you are seeing this, please lock it.