FYI ever since performing the opkg upgrade, I’ve not seen this issue occur.
There seems to be a small glitch in the opkg upgrade procedure; the new kernel “kernel-image-3.8.8” refuses to install since it overwrites some driver files provided by the old kernel-image-3.8.6, so you have to manually install it:
opkg --force-overwrite kernel-image-3.8.8
I found this out only after I put my BBB into a non-bootable state and had to recover it (with the uboot command prompt, forcing it to boot the old kernel).