Hello,
There are some problems in your script logic. You do not handle the events correctly or not at all ($EVENT:ONINIT$, $EVENT:ONREOPEN$, $EVENT:ONUPDATE$). Sometimes, you execute the functions twice and this results in an unexpected behavior.
To fix the problem from the question asked, add the %DEST_DIR% runtime variable to the Static Text field. Then remove the Set Text "%_SB_INSTALLDIR%" to ControlID "DESTFOLDER" line from the script. But again, there are some more problems in your script logic. This will only fix one of them.
Does this help?
Friedrich
P.S. NEVER create a folder from within the wizard that collects information from the user. All this should be executed after the wizard.