Party frames have a hard time updating if players join your group while you are in combat.
There were two in my group already and two others got invited and joined while I was in combat. The party frames "shifted" as if the new frames were added but they were not visible.
I attempted to fix the display by first using the options to disable party frames and then re-enable them which didnt work. Then I tried leaving the group and re-joining it which also didnt work. Lastly, I reloaded my UI while in the group and that corrected the group display.
Id think this is a low priority bug at best, definitely not game breaking anyway.
If you decide to allow in-game on-the-fly changes to a frame, perhaps you could allow the loading of preset config files that a user can select. And to build on that idea, you might add an export function to create these preset config files.
These config files could be very similar to the current layout files that we use today and could even include more preset control over in-game options.