Oh, what a tangled basket we weave....

I've done my own fair share of bungling about the Cloth Room, & fer what is worth, here are my observations on yr predicament

DISCLAIMER
My experience has been w/ P5 & lately P7....P6 may (shockingly as it may seem) contain it's own glitches of which I am unaware. But the followin' advice looks good on paper, anyway.

OK.....Fer starters, the Zero pose ting. I sorta agree w/ markschum way up there ^^^ 'bout checkin' yr Keyframe Editor. However if thas the culprit, I'm tinkin' there's gotta be @ least 2 frames (prob'ly 29 & 30) to ditch; Frame 29 being "in pose", & Frame 30 being zeroed. If it was only one zeroed frame, you'd notice the motion towards zero in yr animation.

"and drag the selection box around all the keyframes at frame 30. Then press the delete key."

Actually, there's a easier way. Just scroll to the very top of yr Keyframe Editor, & above the scene actors, there's a 'nother row (easy to miss) that'll select everything in a given frame. Notice also that any actual keyframes are a brighter green, so if yr last frames are a dark green, this prob'ly ent the probbem.

If all else fails, ya might wanna just kill the last frame of yr simulation (or whenever it's snapping to zero).  Open yr Simulation Settings & set the End frame to 29.

Now fer the intersectin' clothing.

It sounds to me like the clothing in question has built in morfs & a matching pose set fer the figure. If these don' match VERY closely if not perfectly, yr gonna have probbems. Guarunteed (in my experience). I favour the method described by purdy much every one else & start the figure & cloth from a zeroed pose (whether or not ya use the Start from zero pose checkbox), & add the pose at frame 10 or so.

The use of the Soft decorated group is baffling me. Actually, I gonna give it a try, but as far as I can see is kinda pointless. The why of which is prob'ly easiest to explain by describing all the groups;

-Dynamic Group: the main "body" of yr clothing item

-Choreographed Group: Advanced animation use....fer now, just don' use it. Is a PITA

-Constrained Group: A selection that will not move from is position relative to the figure. Works well fer shoulder straps ya don' want fallin' off shoulders, button flaps or necklines ya don' want openin', etc.

-Soft Decorated Group: A selection that is somewhat more rigid than yr base material that will stay in position relative to the clothing itself. Good fer pockets, cuffs/collars, belts, etc.

-Rigid Decorated Group: A hard selection that will stay in position relative to the clothing. Buttons, medals, etc.

So.....w/ all yr newfound knowledges (pronnounced Kin-fyoo-zhun ;) yr workflow should look kinda like so...

1. Load figure. Zero any pose, turn off IK, & drop to floor
2. Load dress. Tweak fit if/as neccesary w/ XYZ trans. Parent to figure (optional; the dress is gonna collide w/ what is told to regardless of whether is parented)
3. Load Props
4. Set pose somewhere in the frame 10-15 range
5. Go back to frame 1.
6. Go to cloth room
7. New Simulation
8. Clothify dress
9. Collide against figure
   -  uncheck head, hands, feet if you don't need those
   -  be sure to select Ground if yr usin' a trailing dress or robe, & any other prop/figure that may come into contact w/ yr sim
10. Check yr cloth groups fer "unwanted" or "surprise" groupings. Edit as desired/required
11. Save the file
12. Cross yr fingers
13. Calculate Simulation
14. Pour a coffee, grab a book, play w/ yr cat fer a while.....
15. Scream "YOU ^#!&%% piece of &%^%)(&%!!!" in frustration when the sim is done 'cuz ya missed step (X)

A final note; If, while yer fitting yr clothing to yr figure (Step 2), ya notice any pokethrough issues...DO NOT try to remedy it by turnin' off body part visibility w/ the heirarchy editor as ya might w/ conforming clothing. This will make the cloth room not "see" the part at all & cause it to not collide.

Fer a bit more Cloth room info, I have a kinda-sorta mini-tut tingy here from a while back

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2137231

WARNING!

This user has been known to swear. A LOT!