I notice a few odd issues when applying Master B with replacing Master A but migrating its content. Both masters are independent.
1 of 2 picture frames appears visually as expected. Its frame has same size and position on both masters.
The picture frame of the new master at this position isn't transferred (~ replacing the former) but replaced with the existing of master A.
The other picture frame becomes
– set to invisible,
– scaled in width,
– its image gets horizontally moved
Wow! In Beta 651 it works like a charm and even auto-migrates accordingly to layout variants between two masters.
I am really impressed, it appears close to "Smart Master Pages" without their need of manually named layers and resources!
master replace existing w pict-frms_beta651.m4v
(NOTE: Since the beta usually handles former file versions as well, one should know that it seems not to work in this case:
If I use my .afpub from v183 then beta 651 causes exactly the same issues. So,