Slide duration after applying style/theme

[SeismicGuy]

It has been a while since creating a vacation slideshow so I may have asked this before but just forgot the answer.  If I place slides in the slideview line or timeline and set the duration of each to be some consistent number (e.g., 8 seconds) but then apply something like the Ken Burns theme to some or all of the slides the duration of each changes.  This works sometimes but sometimes not so I need to go in and tweak the durations on the slides.  I assume the duration change is by intent depending on the style/theme being applied, but is there any way to lock the durations?