Whoops, actually I did get a reply from SiLabs few days ago but it ended up in my spam box.
Looks like people with USB issue better get a xacto knife out.
The fix (though not software) is luckily easy enough:
Since its right next to USB lines, be careful.
Explanation by SiLabs:
Originally Posted by silabs guys who actually read datasheets
Looking at included schematic, you've connected internal 3.3V reg output (VDD) to VBUS, in bus-powered situation it should be left NC.
My own interpretation of the above, hubs "fixed" the problem by causing voltage to drop just enough below 5V to let the system operate in-spec.
If you're afraid to cut traces, you can take a USB cable, find the power wire, cut it, and put a diode in series to drop 5V to some lesser levels.
If neither of the options are acceptable, you can send it here for surgery.
Needless to say any newer boards will go out with that fix already included.
Actual board example:
edit: just checked my other "dodgy" CP2102 device - looks like I'm not the only idiot who can't read datasheets, they have it connected same way. There must be just enough voltage drop on afro board vs a plain old usb>serial dongle to make one work and not another.