Cannot set Spark Label or Spark RichText showTruncationTip property at runtime using bindngs or ActionScript

Found in 4.0.0.13383.

Steps to reproduce:
1. Compile and run attached MXML file.
2. Roll over the Label and RichText controls and note you dont get any tooltips (correct).
3. Toggle the CheckBox to set the Label's showTruncationTip property using databinding.
4. Toggle the ToggleButton to set the RichText's showTruncationTip propety using ActionScript.
5. Roll over the Label and RichText controls and note you still dont get any tooltips (incorrect).

Actual Results:
You cannot change the showTruncationTip property at runtime.

Expected Results:
You should be able to toggle truncation tips at runtime.

Workaround (if any):
Set it directly in MXML to a static value and dont try changing it at runtime.