Windows 7: AMD high-definition device switching HDMI/Local-Speakers/Headphone

gang
I hope someone can help me with this - its the worst kind of problem due to inconsistency: sometimes the system works as it should, other times not.
Windows 7 home premium on a thinkpad x120e. I and my thinkpad go a lot of places, and in many cases thanks to stability of Windows 7 [ahem] I am not restarting/rebooting, or logging off very often. so, when docked, I use hdmi-out to a bigscreen and its associated audio setup. sometimes I unplug from hdmi& use headphones, and sometimes just use the builtin spkrs. usually the transitions, audio-wise, are all correct, but not always. Unplug from HDMI, plug headphones in, and instead get onboard spkrs.

I have no other audio issues that I know of - sound is good, just in the wrong output device/speakers/whatever