Writing in Doctor Who Magazine, Steven Moffat teased further answers on the matter in the new series, stating:
“As the Type 40 bad girl made clear in The Doctor’s Wife, she doesn’t like him bringing home strays. The TARDIS, as we know, likes to fire her pet Time Lord at interesting moments in history and watch the fireworks. Anyone less mad than the Doctor might have noticed by now the TARDIS navigation always works perfectly when the crisis demands, but never when he fancies lunch, or tea and biscuits at the Eye of Orion.
“Now those pesky humans who keep following him home are usually content to stumble about, saying: “It’s bigger on the inside.” and remain sufficiently in awe of the Police Box magic never to question it. But clever, sceptical, hard-to-impress Clara might just cause trouble. It’s almost like it’s all building to something… Oh! What’s this I’m writing today?”How do you want to see this plot point resolved? Comment below!
[Source: Doctor Who TV]