CategoryList property on IList is not supported?

This property on a BlockData type:

[Display(
	Name = "Predefined groups",
	GroupName = SystemTabNames.Content,
	Order = 20)]
public virtual CategoryList Groups { get; set; }

Causes errors when the block is used as an IList<MyBlock> property. 

[
    {"severity": 3,"errorMessage": "\u0022.2398(0).2470.\u0022 is not a valid value for \u0022Predefined groups\u0022."
    }
]

Is categorylist not supported?