How to fix a Macbook that does not always draw its internal screen after waking from sleep and having unplugged external display while asleep?
I would pay attention to two factors:

1) Do you have an external keyboard attached?

2) The power situation - how/when sleep happens is affected by this

3) If the lid is closed at the time you move the mac.

A couple of examples will help illustrate this:   

Recently I found that my external keyboard was not waking up the closed lid mac as I thought it should.  I found that this was because the power was unplugged and the 'lid closed' operation only worked with the power actually plugged in.

As another example I found that when my computer was asleep, in order to wake it up - without opening the lid! - the trick was to plug an external keyboard/mouse in and hit a key / move the mouse.  This then took the mac out of sleep (though again that may depend on whether you have power plugged in or not).