Captions with "mystery scrollbars"

I have a project where all captions are working well, except for two of them.. They somehow have vertical scrollbars. They are configured the same way as all the others that don't have the scrollbars. I tried copying other captions that are working properly and replacing the text. I tried "format painter" with other captions that are working properly. I can't figure out why the scrollbars are there... 
Strange, that they appear only when viewing the project or scene. If I preview the slide by itself, they "behave properly."