show longwhich should show a default value of 80 if you never overrode it in your connection login script (Tools | Preferences | Database). So just
set long 4000and try running the script that outputs the XML again. Keep in mind that set long
Sets maximum width (in bytes) for displaying LONG, CLOB, NCLOB and XMLType values; and for copying LONG values.Possibly Bug 5904607 needs revisiting, but I hope the approach described will be sufficient to get you past the current problem.