Library /sys$common/syshlp/dbg$help.hlb DEBUG, CANCEL, SOURCE, Qualifiers, /EXACT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Cancels the effect of a previous SET SOURCE/EXACT command, which
    specifies a directory search method. Canceling this command means
    that the debugger no longer searches for the exact version of the
    source file from compilation; it reverts to the default behavior
    of searching for the latest version of the file.