I ran into this during the weekend while I did some work from home. The site I was working on is running EPi6r2 with PageTypeBuilder and I was just adding a couple of new properties for a page type when I suddenly and unexpectedly got the yellow...

Since EPi CMS had property types with custom settings added I have found the drop-down list ( EPiServer.SpecializedProperties.PropertyDropDownList ) especially useful for allowing an editor to choose from a few different teaser content block...