Patch due ahead of launch. http://www.bit-tech.net/news/hardware/2014/05/28/surface-pro-3-charging-flaw/1
Software update to fix charging issue...... Charging should be Hardware based and you should be able to use plugged in no matter the state of the battery. This is a major design failure. Though I fear this is done on purpose to shorten the product life span.
You can't rely on a purely hardware based charging solutions with modern batteries, unless want a lot of exploding batteries. There needs to be a software element to it.
OK "software" as in a few lines on code on a control chip not integrated into the OS or BIOS which can only send info but not receive and I am not convinced this can not be done with a decent circuit. either way there is no excuses for a device that can not take all required power from external source. Many an old laptop I ran without the battery years after it was no longer useful as a full windows PC.
If that would work it would have been done. There is quite a bit of negotiation going on between a charger and a battery to allow for rapid charging, but not over-charging, of the battery in any state while minimising memory effects and maximising its lifespan. The device meanwhile has to use that power as sparingly as possible to make the battery last. Your old laptops had brick-like batteries that lasted for three hours tops. That ten-hour lifespan we enjoy now? It ain't down to the battery; it's down to the technology that manages it.