The weirdest thing just happened. I can't reproduce it anymore but thought about reporting this.

I have this page type which has five properties as shown below. ContentSelectionAttribute's code took from here.

        [ContentSelection(typeof(ResponsibilityAreaType))]
        [Display(
            Name = "Type",
            Order = 1000)]
        public virtual PageReference ResponsibilityType { get; set; }

        [ContentSelection(typeof(ResponsibilityAreaContact))]
        [Display(
            Name = "Contact person",
            Order = 1100)]
        public virtual PageReference ContactPerson { get; set; }

        [BackingType(typeof(PropertyMunicipalityListing))]
        [Display(
            Name = "Municipalities",
            Order = 1200)]
        public virtual PageReferenceCollection Municipalities { get; set; }

        [Display(
            Name = "Link",
            GroupName = SystemTabNames.Content,
            Order = 1300)]
        public virtual PageReference Link { get; set; }

        [Display(
            Name = "Link text",
            GroupName = SystemTabNames.Content,
            Order = 1350)]
        public virtual string LinkText { get; set; }

I was running the page in debugger and editing stuff in form designer. For some reason, don't remember why, I hit F5 to refresh the whole page. This is what happened.

Link property that should be normal PageReference selection control has turned to dropdownlist, and somehow it gets it's content from ContactPerson property's list (the items are identical).

I tried to refresh the page again but it didn't settle. I switched to other page (in edit mode) and back again and still it was showing dropdownlist. I was losing my mind until I had an epiphany to close browser window, stop debugging and restart Visual Studio. After that everything went back to normal.

Now the thing is. If this happens in production environment, I don't know how I'm going to explain this to the customer and do I have to stop and restart IIS to fix it.