Why did the paint behave this way in Hell Bent?

Question

In an episode before Hell Bent,

Clara dies and the doctor is teleported away, leaving the Tardis behind.

We see the Tardis graffitied (presumably by Rigsy) with flowers and a picture of Clara.

In Hell Bent,

The Tardis reappears, graffiti and all, just outside the "diner" where the doctor is talking to Clara

At the end of the episode,

He leaves in it, and all the paint peels off and stays behind

Why didn't that happen when it moved to that location in the first place?

I am ignoring the matter of how it got there - I wouldn't have left Ashildr alone in either tardis myself, but perhaps Clara was able to summon it

Is this symbolic of what he has shed from himself? Is there any reasonable in-universe explanation?

Answer 1

Of course it's symbolic.  It also happens to make perfect sense, given what we know about the characters. 

The graffiti is in remembrance of Clara.  The mundane world probably thinks of Clara as missing, but Rigsby knows that she is dead.  He decorates the TARDIS as a memorial, since he's the only one left behind who knows he has something to remember. 

At this point, the Doctor also remembers Clara, but he wasn't left behind.  He was trapped for uncounted billions of years before he could even try to rescue her.  He survived those aeons and did attempt to rescue her.  During those aeons, he refused to leave her behind. During that attempt, things change. 

Part of the rescue attempt would involve making Clara forget about the Doctor.  She is unwilling to lose those memories, even at the cost of her own life.  She sabotages the memory-altering device.  Knowing the sabotaged device was unpredictable, the two agree to use it.  As a result, instead of Clara forgetting the Doctor, the Doctor ends up forgetting Clara. 

The Doctor is aware that he's forgotten something.  He spends time talking to a stranger (who happens, unknown to him, to be Clara herself) while he tries to decide whether to chase the missing memories or simply leave the forgotten person behind.  In the end, we suspect he decides to leave the lost memories unexplored. 

He doesn't say this out loud.  He simply hops in his TARDIS and vanishes. 

The TARDIS is a character.  She's sentient, sapient, mentally connected and emotionally bonded to our beloved protagonist.  She is able to think and act on her own behalf and in her theif's best interests. 

Prior to this moment, the TARDIS preserved the mementos.  If the Doctor had decided to chase these memories, the TARDIS would likely have continued to preserve them.  Why not?  It's easy enough for her to keep them inside her integrity field. 

Of course that she doesn't is symbolic.  We've seen Clara escape the end of her own story several times.  The writers had to give the audience some signal that says "her story is over -- and we really mean it this time".  From a Doylist perspective, the symbolism is unavoidable. 

The reason that it works is that the TARDIS is a character.  The Watsonian perspective makes sense.  When we see that the mementos are left behind, we understand that the TARDIS agrees with the Doctor.  Maybe the Doctor leaves Clara behind by accident, but the TARDIS leaves her behind on purpose.  She is supporting his decision.  Because the graffiti is left behind, the audience understands that from the TARDIS's perspective Clara's story has (finally) ended. 

The TARDIS leaves behind mementos of someone that she agrees that the Doctor shouldn't try to remember.  Before that, she kept them around because she hadn't made up her mind or even considered the question.  The only explanation I need is that the TARDIS is doing, at each moment, what she feels is best. 

Answer 2

Warning: speculation.

The Doctor's TARDIS need not have dematerialised to get there. If Clara had previously materialised "her" TARDIS around it, she could have brought it with, and had it separated from the Doctor by an interior wall in the scene in the diner. When she later dematerialised hers, leaving the Doctor behind, she could have left his TARDIS too. Only when the Doctor's TARDIS dematerialised, this time under its own power, did the paint fall off.

Of course, this is still inconsistent with some other instances of things sticking to the outside of the TARDIS while it was in flight. Jack Harkness hitched a ride that way once, and there's been an instance where the TARDIS was covered in flyers, which caught fire but stayed attached. Then again, Stephen Moffat's inter-episode continuity has always been spotty at best.

Answer 3

It would seem to me that the original now painted Tardis was transported inside the other Tardis, and therefore it retained the paint job because it was merely an object being moved inside a Tardis, and not performing the time travel itself. We see the Tardis shed a number of flyers that were affixed to it way back in the days of Rose, when it leaves from near her apartment in one episode.