I was trying to show my twin sister how you couldn't go in a TARDIS when you're already in a TARDIS. So I placed the 80s TARDIS in my  2013 Dalek Mod B TARDIS Interior, and I went to open it to show my sister that I couldn't, but it let me in! I was surprised, and when I left the 80s TARDIS Interior, I was back in the 2013 Dalek Mod B Interior (this was the 1.8 mod, so they were both the same looking interiors). And I paused the game to go do something, and when I came back, I had forgotten that the last TARDIS I was in was the 80s TARDIS, so I went into Flight Mode in the 2013 Dalek Mod B interior, which I had not left. I was then flying around the TARDIS Interior with the 80s TARDIS, and I thought it was cool at first, but then when I tried to land, I couldn't. I realised I probably couldn't land because I was already in the TARDIS. And since I had no way to leave Flight Mode, I tried to get my player killed in every way possible. I even used LAN to get my sister into the World so that she could use commands to instantly kill me, and to put me in Survial Mode so that she could kill me with fire, and she even used the Sonic Blaster to drop me into the void! And I just kept falling, with no death. I had to fly back up to the TARDIS Interior and try something else. It wouldn't let my sister build a nether portal in the TARDIS, and I had no way out. Eventually, I ran the game without the mod and went into the world. I died quite a lot (kind of like Captain Jack), but I was free. I had to reinstall the mod and start re-doing everything I'd done to customise my TARDIS, which was a lot. So now it's been 2 days, and I haven't done half of what I had done before   I have a backup of the version of the world where I was still stuck in Flight Mode, and if there's any other solution to this problem, please let me know so that I can apply it to the backup and get my progress back!

Wow, never heard of that happening before!! I've tried to enter and it hasn't let me so how did it let you!?

I've had this happen to me before just exit and enter the game that fixed it for me

 I've tried that and it still won't let me land the TARDIS in the TARDIS. The only glitch that that fixes is the one where the demat lever stops working and my TARDIS gets stuck in flight.

Well then i can't help you

 The 80s TARDIS was always the WIP one. When you go into it, the door doesn't open like it does for the other TARDISes; you just go in. What I think is that the mod uses a protocol to prevent a TARDIS door from opening while in another TARDIS Interior, stopping your entry into the other TARDIS. But since the door of the 80s TARDIS doesn't open when you go in, the mod wouldn't recognise it as you trying to go into a TARDIS within a TARDIS, so it would let you in. And since the TARDIS Flight Panel makes you fly the last TARDIS you went in, it put me into Flight Mode with the 80s TARDIS while I was in the Interior of the 2013 Dalek Mod B TARDIS. And apparently you can't land a flying TARDIS within another TARDIS. And there's no way to go to another dimension while in Flight Mode. Especially since there's no Time Virtex Manipulator in the Dalek Mod's 1.8 version.

 That's okay. Thanks for trying to anyway. Anyone else know another way?

Tried an explosion?

This happened to me on the private server. I don't know of a good way to do it on LAN, but I got out by being teleported by a friend to the overworld, disconnecting, reconnecting and dying a heap. Just don't go back to the TARDIS Dimension for a while... I had to do it 4 times, because I kept going back into the TARDIS...