Originally Posted by Turbotronic

The RF chip used was originally intended for low power devices like keyboards and mice. It was marketed as "wireless usb".
There is a function on the chip that would allow the chip to boost its input voltage to ride out brownouts much better.
The vendor explicitly states that if this function is not used the relevant output pin MUST be grounded and not left "floating" ie unconnected.
Well floating it is on spek's where it acts as a source of poor power regulation and a random input of RF and EMI to the RF subsystem.
Ironically some of the clones do have this properly grounded.
Its not my opinion but that of the chips vendor technical department application engineers as confirmed to me when I raised a query about this.
You should check with Spek if they have since corrected this when I pointed it out some 5 years ago.
Its a ridiculously easy fix to do.
As the mfr will tell you the fail mechanism is unpredictable but will certainly cause the RF chip to brown out randomly, depending on the environment it finds itself.
But I suspect it also degrades the RF link in some way regardless of power conditions.
Its perfectly OK for a foamy I would think...