I found a Polar USB hub with AC adaptor.

Shorted data+ and data- pins of one USB port after isolating them from
the hub's chip.

This time, the USB hub is being powered ONLY and directly from its AC
adaptor, rather than using an AC to USB adaptor.

It works, including hot-plugging.

SO the problem might be the AC to USB adoptor.

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.39.1
^ ^ 18:31:01 up 1 day 21:50 1 user load average: 0.31 0.17 0.10
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_...sub_addressesa

> This time, the USB hub is being powered ONLY and directly from its AC
> adaptor, rather than using an AC to USB adaptor.
> It works, including hot-plugging.
>
> SO the problem might be the AC to USB adoptor.

I went back to the other USB hub, chopped the data+ and data- pins at
the input USB port that's connected to the AC-to-USB adaptor.

The charging instantly started working, including hot-plugging.


--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.39.1
^ ^ 17:35:01 up 3 days 20:54 0 users load average: 0.00 0.03 0.05
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_...sub_addressesa