An extended type can change variable types?

Again, armed with the knowledge I have been newly given by FlameDuck, I guess this makes sense. Kind of surprised me, though.

Strict

Type MainTypeData
	Field name:String="MainType"
End Type

Type ChildTypeData
	Field name:String="ChildType"
	Field iamdifferent:String="I am different!"
End Type

Type MainType
	Field data:MainTypeData=New MainTypeData
	
	Field bleh:Int = 1
	
	Method CreateThis:MainType()
		Return New MainType
	End Method
End Type

Type ChildType Extends MainType
	Field data:ChildTypeData=New ChildTypeData
	
	Field bleh:Float = 7.51
	
	Method CreateThis:ChildType()
		Return New ChildType
	End Method
End Type

Local Main:MainType=New MainType
Local Child:ChildType=New ChildType

WriteStdout(Main.data.name+" bleh is ")
WriteStdout(Main.bleh+"~n")
WriteStdout(Child.data.name+" bleh is ")
WriteStdout(Child.bleh + "~n")

WriteStdout("This is a variable in an object created by the MainType.CreateThis method: " + Main.CreateThis().bleh + "~n")
WriteStdout("This is that variable in an object created by the overrided ChildType.CreateThis method: " + Child.CreateThis().bleh + "~n")

End

Same example, this time overriding method return types.
What I am seeing there is: As long as the overriding method's return type is based on the return type of the method being extended, it can happen. I find it strange that this does not happen with other types that can be converted, like Floats and Ints. (Only with custom types, it appears).

I realize this is really not much over what was already possible, but it saves a lot of typing!
I can't believe I spent a year ignorant of this.