When you select Popup Menu as the control style for a field on a layout and the value list is defined to use values from a first field and a second field, where the option is chosen to show only the values from the second field the desired result is that the selection of one of the values results in the second field appearing the popup menu, even though the actual value in the field is that of the first field in the value list.
For example, if you have a value list vegetables, where the first and second field are like this;
Then, choosing Carrots in the popup menu will result in the value "3" being in the field while the word "Carrots" appears in the user interface to indicate to the user that they have selected Carrots.
This is not the case with drop-down menus, where the field value displays the first field in the value list, not the second.
Now, here's the problem and the workaround in FileMaker 15.
If you first specify the field as a Popup menu, you will find that the user interface displays the first field, not the second field, when a selection is made. That is, if you choose Carrots, the popup menu will display the number 3.
But if you change it to a Dropdown List and choose the option to include the arrow, and then change it back again to a Popup menu, then you get the desired result.
I can't figure out what is making it behave this way, and I don't mind using the workaround now that I know what to do, but it's a flaw.