First of all, I don't know if you are doing it right. But I'm not sure what you are trying to achieve by having users add multiple values in a dropdown. The dropdown should provide you with the option to select one value, and maybe add a value if the value you need is not present.
You can also set a value list up to take all the values entered in that field over all records.
But to try and answer your question: Have you looked in the inspector in the data tab?
There is a section that allows you to choose which keys will bring you to the next field. You can check or uncheck "Tab", "Enter","Return"
Maybe you could have a look at what is checked right now.
I have looked at the inspector behaviour but that is tabbing to the next field not what I am looking for although I have tried checking both options or unchecking both options and it doesn't help.
The user wants to add a value to the drop down as it is not present therefore clicks edit at the bottom of the drop down list, this opens a pop up box of the value list, if one clicks on the enter under the backspace it goes to a new line in the value list pop up box, however if one clicks on the enter under the Numlock it closes the value list.
I want both enters to go to a new line in the value list not close the value list pop up box. I am sure this is possible, I just can't figure out how to achieve this.
I don't believe that can be changed. That is just normal behavior for all dialogue boxes.
But if you do find out how to get this done, please let us know.
It's not an option for you. Like many dialogs from many different software packages, pressing Enter (in the number keypad) is the keyboard short cut for clicking the dialog's default button. This is not an option you can change from within FileMaker.
You might consider not using a custom values value list but rather a use values from field value list. This requires more design work on your part to make it user friendly, but you can now set up a system where the user addes new records to a portal as a way to modify the values shown in the value list.