The documentation (WiX Documentation, accompanying the Windows Installer XML Toolset 3.5) explains the Property attribute of the Control Element thus:
"The name of a defined property to be linked to this control. This column is required for active controls."
My understandning of this explanation is, that the value of this attribute should be the name of the Property, that will receive the updated value in the type of Control, exemplified below. This is, however, not the case. Instead, it appears this property value should be the name of a property, that contains the name of the Property to be updated by the Control. The following lines of code demonstrate the entities involved:
<Property Id="UITEM1" Value="ITEM1"/>
<Control Id="MyId" Type="Edit" X="100" Y="199" Width="64" Height="17" Text="<span>[TITEM1]</span>" Property="UITEM1" Indirect="yes">
<Custom Action="TITEM1" After="InstallFiles"/>
<CustomAction Id="TITEM1" Property="TITEM1" Value="<span>[ITEM1]</span>" Return="check" Execute="immediate"/>
I regard this as a problem, either with the compiler (candle) or the documentation. However, I am too new to WiX to see, whether I have overlooked something.