Hello Jaime,
This happens because your folder property is a
private property (i.e. contains lower letters in its name - SqlTrustedConnection). To achieve what you want you should use a public property name (i.e. SQL_TRUSTED_CONNECTION).
When the installation passes from the dialogs stage to the install execution stage the values (set during dialogs stage) of the private properties are reset to their default values. This is the behavior of Windows Installer. Only the public property values are preserved when the installation passes from dialogs stage to the execution stage (i.e. after pressing the [Install] button).
Let us know if this helped.
All the best,
Daniel