In contrast to previous versions, GuiXT now processes the screen with its GuiXT script after the search help selection. In your script you have the statement

Set V[z_me3xk*] ""

which clears the fields after searchhelp return. Even with previous GuiXT versions it would be a problem if the user activated a SAP standard function (such as /O to display the session overview) and then returned to the screen, loosing all the input values.

I suggest you check the transaction id before clearing the fields, for example with the following script lines:

// new transaction? then clear fields
if not V[_transactionid=&V[me3xk_transactionid]]
 Set V[me3xk_transactionid] "&V[_transactionid]"
 Set V[z_me3xk*] ""
endif