600m Hosting Multiple USB 2.0 Powered Hubs

I am attempting to host 4 - 7 port DLink USB 2.0 Hubs (all powered) each with 6 USB 1.1 HID devices connected.  The USB 1.1 devices are bus powered at < 100 mA each.  They each have an Interrupt IN endpoint w/ a polling interval of 4 msec. The 600m seems to have a very difficult time reliably enumerating all the HID devices.  In some cases it will work properly, but in many cases it won't.

I have read some comments about the 600m have problems supplying adequate power to external USB devices (e.g., hard drives), but that should not be an issue here since all hubs are powered.

Any insight?