Kray,
Here's the specifics on my rig and then I'll offer some ideas as to what went wrong. I've used the following rig 4 days this week and had zero twist problems.
Butt: 4-5' of 20lb Stren Big Game (or whatever, it is just stuff I bought at wally world).
Stops: 5 turn nail knots from an old 6 weight line.
Indicator: 3/4" Thingamabobber
Mid/bottom: 4+' of 6 or 8lb 100% fluoro P-line attached to butt via a tippet ring.
Tippet: 6 or 4lb 100% fluoro P-line.
Weight: Appropriate size and number of shot positioned just above the mid section-to-tippet connection knot.
As for your twisting problems, I think there are three possible problems that stand out:
1) The stops could be jammed against the thingamabobber too tightly and it is not turning freely around the leader. You could probably get away with leaving a 1/4" or so of play between the stops so that the TAMB moves very freely at the desired location on the butt.
2) The stops themselves are two small in diameter and are jamming into the loop on the TAMB and preventing it from spinning freely when casting or picking the line up from the water. Using a thicker piece of fly line could solve the problem.
3) The flies are twisting the leader. I've had problems with some larger rubber legs nymphs twisting up tippets in the past.
Of the three, I think #1 and #2 are the most likely . It's hard for me to say since I've had zero trouble with the rig so far except that I think i will be making some 30lb butts as the 20lb mono is a little light for casting heavier rigs with bigger flies. I think 30lb coupled with a heavier mid section will do a better job with turnover in some situations. That said, I fished all larger sized streams this past week and did well with the rig.
Like I said, I've had no trouble with the rig other than the nail knots on my first rigs sliding too easily. That was solved by adding a turn to the nail knot in order to increase grip on the butt. My suggestions are only based on educated guesses. There are a limited number of things that could be causing the twist. It's either the TAMB no turning freely or the the twist are coming from somewhere else. If it is the flies causing the problem, perhaps swapping out a small swivel for the tippet ring (or whatever connection you are using) could minimize the twist.
Kev