mandacaju There's not much to elaborate on really. No, EA has made no statement that I know of. They have never worked indoors in a vanilla game. They only work on the outside of an exterior wall. You can't even select one to apply on an interior wall. It just goes invisible and won't place. Basically, friezes are designed to be used just like their RL counterparts. Outside, you use friezes at the top of the highest wall just under the roof line or in combination with spandrels on roofed porches. Indoors, you use moldings at the top of walls where they meet the ceiling. In almost all cases moldings are much smaller than friezes although they can look the same. Dental friezes and molding are widely used and are identical, just different sizes for instance. Although, in some building styles moldings can be larger depending on the era the building style was in fashion. In the game, there are times though when friezes will intrude into a build if the game sees the wall on the inside or around the stairwell as part of the exterior wall. Stacked open stairwells where one or two walls are the exterior walls are good for that. But mostly, that depends on the order in which the builder does things.
I can understand why you might want to use them since we don't have ceiling moldings. I wouldn't simply because the majority of them are too big, and you can't scale them down to an appropriate size. It's just one of those beauty in the eye of the beholder type of things. Bottom line is if you want to use them, that's your choice. All I was trying to say was they weren't designed to work that way and that is why you got the weirdness with them so it's not a bug, that's all.
If it is something you feel strongly about and would like it changed at some time in the future though, you would be better served to post in the The Sims 4 Feedback | EA Forums. which is the section of the forum for those types of things.
Hope this helps.