Description: If you select a field in layout mode and convert it to a button (i.e. to "goto related") or if you group fields together or labels together, you cannot change the style/font/font size/color/or decoration of the objects in the group without ungrouping the objects or individually selecting each one in the Layout Objects panel. This can be extremely tedious in maintaining legacy applications which do not utilize custom themes and styles, but which have myriad fields which are already goto related buttons (and hence part of a group).
Workaround: Change these settings before grouping. I haven't tried applying a custom style and then changing the style, but I assume that might work. If you have too many fields already grouped as their individual buttons, you have to perform these edits in FileMaker 15.