@teto, solution for ya since I had the same obnoxious issue as I like to run 3 or 4 terminals in scratchpads...
here's my bindsym for three of my scratchpadded items.
# quake style terminals
# top
exec .local/bin/urxvtq scratchpad_urxvt_top 180x28
for_window [instance="scratchpad_urxvt_top"] move to scratchpad, border 1pixel
bindsym Mod1+i exec .local/bin/urxvtq scratchpad_urxvt_top 180x28, [instance="scratchpad_urxvt_left"] move to scratchpad, border 1pixel, [instance="scratchpad_urxvt_bottom"] move to scratchpad, border 1pixel, [instance="scratchpad_urxvt_top"] scratchpad show, move position 45px 0px
# left
exec .local/bin/urxvtq scratchpad_urxvt_left 100x50
for_window [instance="scratchpad_urxvt_left"] move to scratchpad, border 1pixel
bindsym Mod1+a exec .local/bin/urxvtq scratchpad_urxvt_left 100x50, [instance="scratchpad_urxvt_top"] move to scratchpad, border 1pixel, [instance="scratchpad_urxvt_bottom"] move to scratchpad, border 1pixel, [instance="scratchpad_urxvt_left"] scratchpad show, move position 0px 25px
# bottom
exec .local/bin/urxvtq scratchpad_urxvt_bottom 180x28 "journalctl -f --full"
for_window [instance="scratchpad_urxvt_bottom"] move to scratchpad, border 1pixel
bindsym Mod1+j exec .local/bin/urxvtq scratchpad_urxvt_bottom 180x28 "journalctl -f --full", [instance="scratchpad_urxvt_left"] move to scratchpad, border 1pixel, [instance="scratchpad_urxvt_top"] move to scratchpad, border 1pixel, [instance="scratchpad_urxvt_bottom"] scratchpad show, move position 45px 350px
The key here is adding the extra:
[instance="item_a"] move to scratchpad, border 1pixel,
BEFORE you trigger the show event. Mine is setup currently to hide either of the other two and then show the selected scratchpad!