VX-8R charging strangeness

Had a strange experience with my new VX-8R yesterday.
The radio was set in its 'fast charger' cradle, but when I went to use it the battery was dead.

I took the radio off the charger and plugged the power adaptor directly into the DC socket on the side of the radio instead. Charging this way causes the VX-8R to show a power bar on the display, and sure enough there were no bars. Leaving the battery to charge through the radio's charging circuit had it back up to full capacity within 3 or 4 hours. This came as something of a relief as it suggests the radio is OK, and so too (probably) the battery. I ran the radio enough to drop the battery EMF by a half volt or so, then put the whole radio back on the charger. After about an hour on the fast charger, the red light was blinking with about a 50% duty cycle and the battery was quite warm to touch. Checking the battery voltage showed 8.2V, the same as the full charge through the radio. I replaced the radio on the fast charger, and after only a few minutes, the red light duty cycle dropped and then (gradually) the green "charged" light illuminated.

So this last behaviour could be construed as normal, but I still wonder:
- Why was the battery dead when the radio was left on the charger in the first instance?
- Why did the uninterrupted fast charge never quite reach 'green' (charged) until I temporarily removed the battery from the charger then replaced it?

Clearly, the radio is working (the the fast charger charges the battery directly anyway). The fast charger is providing a charging current capable of charging the battery at least from some parts of its charge regime (mostly charged). Perhaps there is some odd tolerance mismatch between the this fast charger and this brand new lithium ion battery that prevents the charger from successfully charging it from a mostly depleted condition?

I'm wondering if I left the radio on when it failed to charge on its charger, but then (and assuming it doesn't charge when being concurrently lightly loaded by the radio - which I'm not sure about) wouldn't the radio switch off automatically when the battery charge crossed some lower threshold and wouldn't it begin charging at the full rate at this point? When I found it completely depleted, it failed to turn on at all.

The 'manual' (single side of paper) that came with the charger, and the full radio manual give no clues as to what might be up here, providing only the sketchiest and 'obvious' description of how the battery can be charged. There's not even any mention of the flashing red 'charging' light which seems to illuminate steady when the battery is being charged at the full rate, and then flashes (with a reducing duty) as the battery nears its fully charged condition. Only "red" and "green" are mentioned.

I guess more experimentation will be needed before I can confidently say whether I've experienced a chronic problem with some component(s), or whether this was just some aberration due to odd dynamics of a brand new battery.