TTT MB (The Two Towers MultiBall) rules

Interested in the depth of the ruleset today. Been focusing in on TTT MB (The Two Towers).
You achive it simply by spelling K-E-E-P with the bottom lanes to light locks, then lock three balls on the sword.  Easy? It's more complicated than you think!

Some of this is my own explanation, adapted from the excellent ruleset writen by metallik on RGP:

1. Lock insert is solid when a lock is lit, flashing when TTT MB ready (it's flashing for the 3rd lock). There's not always 2 balls locked on the sword when this happens!
   
2. If setting is EX-Easy or Easy:  Locks can be stacked, meaning multiple K-E-E-Ps can be completed before locking a ball.
   It does this on the first TTT MB, and the ball saver gives the balls back if you haven't scored a Jackpot.
   
3. On the next TTT MBs, you can't stack locks. You *must* lock a ball before the next lock can be lit.
   Always true if Feature setting #4 is MODERATE or higher. 
4. During regular play, if all four letters stay lit, it means you must lock a ball before the next set can be collected.  On the first TTT MB if all four stay lit, that means you have all three locks qualified. It looks unusual when playing, but that's just the way the game rules work.
5. K-E-E-P letters can only be collected during normal play - a multiball saves the state and prevents any more letters from being collected.
6. On later TTT MBs (4th TTT MB or if LOTR Feature adjustment #4 is Extra Hard) KEEP letters will toggle with every rollover.  Meaning if you have letter "K" lit and roll past it, it unlights.  You hear the same "arrow thunk" sound as when draining down outlanes when you lose a letter. Cool effect.

THE TWO TOWERS LOCK DIFFICULTY:
LOTR FEATURE ADJUSTMENT #04

Setting	Locks	K-E-E-P	Lane Memory	Locks Stack
EXTRA EASY	None Lit	2 Letters	Yes	Yes
EASY	None Lit	1 Letter	Yes	Yes
MODERATE	None Lit	1 Letter	Yes	No
HARD	None Lit	1 Letter	No	No
EXTRA HARD	None Lit	1 Letter	Lanes Toggle	No

Note: This adjustment controls how hard it is to light locks.
Default is EX-EASY. Information above is taken from the game manual. Software revisions may modify this in future.

A funny thing I observed:
You can get ALL the K-E-E-P lights frozen solid and they stay on even when all the other lamps other go dark.  Both GI and controlled, for “Path of the Dead” or any of the other modes.  It cleared after scoring TTT MB (The Two Towers).  Then you are back to no balls locked and no K-E-E-P lights lit and plays normally from there. I have also seen that at game over the attract mode will clear locked K-E-E-P lamps. So the CPU is KEEPing (ha!) them lit.  If it's a software bug, setting LOTR Feature #4 to MODERATE (or higher) hides it.

Perhaps it was the first time I had ever qualified for TTT MB, by stacking the 3 locks but without locking a ball? (See 4th bullet point above). A weird effect you get from holding the K-E-E-P lamps on when a lock has been pre-qualified.  Any one else seen or understand it?

Finally a possible software bug:

My LE game has the latest CPU ROMs v10.02, as delivered from factory Dec 2009.

I noticed that when the LOTR Palantir awards a "Spot K-E-E-P letter" it doesn't add one. You get the display, but a letter doesn't get lit by the Palantir.  Maybe makes earning locks harder, or a feature not implemented correctly?

I have written to Stern and am waiting to see what they say. Got first reply 19th April 2010.  To "check the lamps #1-4 were lighting in the single lamp test." Yeah, they are and the lamps all work exactly as they should.