If you don't mind the risk you are fine. I'd play safe and flying into Cambodia or Laos and then border cross. They won't stick you on a plane back to the UK/US or whatever at a border checkpoint.
The concern I have with issues like this is when the rubber hits the road, you are going to be at the mercy of the immigration officer's understanding of the matter. You may be 100% fine.
Thanks Tod. Weird thing I was expecting a three month visa but was given 12. Clearly I had applied for a visa I didn't think I was applying for. Not that I'm complaining mind.
Is there any mandatory time I need to be outside the country? I was thinking of spending two night in Ho chi Min next week.
