If a  a *new* root folder is selected each time a new instrument.
is needed:


¥  a bass, then  selects the Bass root folder.
¥  a drums, then  selects the Drum root
¥  a piano, then  selects the Piano root,


 ......SampleTank will open with the LAST root folder selected.. and, therefore, not able to find all the instrument

so the only work around at this time is after you find the samples that you are going to use for this song, you must create a separate folder for the sounds that you are using so that ST only has to look in 1 ROOT folder for all of your devices...