This feature can only be used in programmed channels - it does not work in the user-defined Limit Search (SR5). The scanner makes additional checks for "valid" frequencies. It has to, so that it can jump between its valid ranges as it's scanning.
UPDATE! You can search through the Extended Ranges! Using Win95, program an out-of-range frequency into some channel. On the PRO-95, select that channel in "manual mode". Press FUNC TUNE. The scanner will no search up (or down) from that frequency. If you let it enter a "valid" range, it won't go back to the invalid range, so you'll have to select the channel and hit FUNC TUNE again.