On each field, while in layout mode, check it's behavior settings on the Inspector's data tab. Make sure that the enter key--which is different from the return key, is not set as the key to exit the field.
WIndows OS Note: on a windows keyboard, both buttons are named "enter". The button that is part of the QWERTY section is the "return" key and the one that is part of the number key pad is the "enter" key. And holding down the ctrl key while pressing "return" will press the "enter" key instead.
Thanks Phil, that was it!