That's odd.
This Craftsman light has that type of lens:
http://www.sears.com/sr/javasr/prod...pid=03493668000&subcat=Flashlights+&+Lanterns
The body is a variation of Dorcy's 4AA Turtlelight. Instead of a single bulb, it has one central 5mm white LED (which is actually potted in a PR base), and 4 additional LEDs arranged peripherally. The bubble in the lens is to create a concentrated spot when the central LED is on. (It looks sort of like the Inova X1's spot)
There are 3 modes: central LED on/peripheral LEDs off = pure spot/no flood, central LED off/peripheral LEDs on = flood/no concentrated spot, all LEDS on = spot+flood
I have a couple to use for blackouts, because the runtime is good, and I like the ability to choose low output/long runtime or higher output/shorter runtime. The beam quality stinks, however.
Anyway (getting back to the original topic), the bubble might be an attempt to improve the intensity of the central spot, compensating for the shallow reflector.