Give this a try, I tested it using FlashFXP 5.4.0.3939 and it appears to work as expected.
Code:
# DESCRIPTION: Create folders on opposite side from the current item selection on the active side.
#
# Display a simple [yes/No] confirmation prompt
/confirm "Create new folders on opposite side using the current selection?\n\n%f"
#This operation could take awhile so display a busy box until the operation has finished.
/busybox Creating folders
# loop for-each name that is selected in the active browser pane.
{
# save %f into variable @f@
/set @f@ %f
# switch active browser pane to opposite side
/switch-activate
# make directory named @f@
# if we had used %f then it would of taken the name from current active side which is wrong.
/mkd @f@
# switch back to the original side before grabbing the next name from %f
/switch-activate
}
# switch back to opposite side so we can update the listing.
/switch-activate
# now update the stale directory listing.
/list
# one last switch to restore active focus back to the original browser pane.
/switch-activate