I've been working on a mobile layout where I'll allow certain fields to auto-size so they stretch to fill out the layout. I'm in FM 16.
My database was created in a prior version, and some of the fields have been set up as Buttons. In FM 16, those buttons become "Grouped Buttons". I clicked on one such field (set up as a button), and anchored it to the top, left, and right sides. The field would not autosize. I then used the Layout Objects panel to expand the Grouped Button, and clicked on the field itself and set the autosize options. It then autosized just fine. If you just click on the field and look at the autosizing setup, it will NOT show the autosizing options that are in effect. This seems like an undesirable behavior.
If I add a field to a layout, set the autosizing options, then turn it into a button, it will autosize properly, and the settings will be set properly. Both the button and the "grouped field" will show the options that are in effect.
At that point, I had my "Grouped Button" set up so that the button was not set to autosize, but the field was. The field autosized. I then changed the Button setup from "Perform a Script" to "Do Nothing." The object no longer showed up as a "Grouped Button", it showed up as a "Group." Interestingly, though the field was still set to autosize, and the "Group" wasn't, the field wouldn't autosize. I ungrouped it (the Group was just a field plus whatever remained after I switched Button Setup from Perform to Do Nothing). Once ungrouped, the field did what the autosizing was set up to do.
I imagine that someone out there will run into this, and will have a bit of difficulty figuring out why a field does or does not autosize as intended. Hope this helps. Also...I'm not sure if I'd call this a bug. If it's intended behavior, I don't really see the benefit of having it act the way it does currently.