To make matters with this interchange worse, drivers using Sat-Nav get sent the wrong direction. Mapping data (supplied by TeleAtlas) on Navman devices has not captured all the necessary layout information for routing through this unusual junction. When travelling North on the A56 and intending to continue on the A56, as you are already aware, one has to turn-off for the A56 to remain on the A56.
At this point during a Sat-Nav guided journey it is traditional for a well spoken lady (or gentleman) to prompt you to "Exit Left" - not on this trip. The weird road layout has not been fully translated and the Sat-Nav forgets to tell you to "Exit Left" for the A56.
Meanwhile, poor unsuspecting driver has sailed straight on and is now halfway to Rawtenstall. Old Sat-Nav suddenly wakes up and realises that it is now on the A682. You will then be sent on an intricate guided tour of Rawtenstall and Haslingden to get you back-on-track (TM). I have experienced this error on Navman devices (ICN520 & N40i) but it may affect other manufacturers too (like TomTom) if the fault is in the Map Data they are supplied with.