Dunno if this is normal or not, but ALL my multi-CR123A lights and battery brands commonly drain one battery more than the other(s), though yours is an extreme case.
It could be dangerous, but in my opinion you need a few more conditions to get the batteries to 'explode' (actually, 'vent with flame' and producing hot gases inside a sealed container, which then explodes), which are difficult to reach in an X5, such as high temps and a high current flow (such as in short-circuit, or a incan light-bulb, which is close to a short-circuit).
I assume that the batteries were already in very different states when you put them in. Also, the X5 as an unregulated light has no real indication if the battery stack is run down, but being a low-powered LED light there is little danger to get a high current out of the batteries, and heat them up with that (which, IMO, is the most common, though still quite rare, condition for 'vent with flame'). I also suspect that the high-voltage battery is pretty dead, too; the voltage is a bad indicator for the charge state of Lithiums.
