I've got some results.
Streamlight says that the light should focus and fire regardless of bezel position - tightened, focused, or removed. They recommended that I return the light to my dealer for direct replacement if bought within 30 days (my case). If beyond 30 days, or if I would rather have Streamlight deal with the problem, they asked for the light to be mailed to them w/ the receipt for replacement or repair. Streamlight claims that this is the first they've heard of this problem.
Yesterday I took my light back to my local dealer. At first they claimed that the light isn't supposed to focus, and isn't defective. They changed their tune after we pulled a fresh one off the display, installed the batteries, and compared it with my defective one. The fresh light focused and fired.
The salesman/tech (tech at the battery specialty store where I bought the light) figured out the problem pretty quickly. Turns out that the switch, bulb holder, and positive battery contact functions are all served by a cylindrical plastic assembly. There are, of course, various metal and electronic components within the plastic assembly to perform the functions. The plastic assembly is held in place within the flashlight body by 2 dots of glue. No screws, milled ledges, collars, retaining rings, or other mechanical means to secure the assembly. The 2 glue dots had let go in my light. Backing the bezel off a bit increased the light length, which allows the plastic assembly to slide away from the battery, which in turn reduces or eliminates contact with the battery. Cranking the bezel back down remakes the connections.
TwinTask owners might want to consider the following:
-- Check your light out carefully. If it has this problem, return it to your dealer or Streamlight for replacement. The xenon bulb casts a much more even and useful beam when focused. You want the capability.
-- I haven't done this on my replacement TwinTask, but it seems to me that the problem is easy to fix for good. Make sure the plastic switch/bulb/contact assembly is in the correct location. Run a bead of epoxy around the perimeter of the plastic assembly to lock it securely to the surrounding aluminum housing. You might want to use a 5 minute gel epoxy to ensure that no epoxy will drip down into the plastic assembly and ruin its operation.
It's still a good and high value light, despite these problems.