So I'm just killing time with my current character having completed the MQ with the Institute. I had very little interaction with Preston and the concord group but since I was trying to raise my affinity with Curie... I figured MM was the way to go. Which btw it is.

Anyway it all started with Preston making me the general and talking about taking back the castle. Now I'm lv 72 with synth grenades so no need to build up the minutemen. Just storm the castle and take it. He meets me nearby and I have them all hang back while I storm in like the hero and clear the whole place out. Got quest updates and everything. Even killed the queen mirelurk.

All is good. Preston expresses his joy at re-taking the castle. And I head on my way.

I map into Home Plate when suddenly I get a quest completion for taking the Castle and setting up the radio, even though I had already done so and had gotten the quest completion. So yay more experience? I thought little of it but decided to go back to the castle and see what was up. I get back there and receive a quest alert to clear out the mirelurk nests... something I had already done. but now taking the castle quest is open again in my data. Well I had already cleared the nests and so the quest would not conclude. So I looked for Preston and found him back in SH

To my surprise he tells me we should take the castle. WTF? I respond with the "already did" response at which he was completely amazed and exited to hear. "I'll meet you there!" he says.

So I meet him there... again. And again I get quest update alerts about setting up the radio and blah blah, all stuff I had already done. The quest then completed giving me now for a third time, experience points as a reward.

But Preston was now so confused and happy that he got stuck with me as a follower. I still had Curie with me but now Preston was following me. When I spoke to him, his dialog was to have him join me. I even tried mapping to the Institute and then out and he spawned next to Curie.

When Bonnie showed up at the Castle is when he finally stopped following me.

Needless to say I enjoyed the quest a lot more then I should have... since I got 3 times the experience from it.

Anyone else had this quest bug out so much?

Wow. Nope. I've taken the Castle with Preston and without him, and in all cases it's proceeded swimmingly. The time I took it without him, I'd have preferred to have left it at that, but it seems the place doesn't clean itself up unless you trigger the quest and get the Minutemen set up there, which I did because I hated seeing the mirelurk hatchling patches everywhere, and I wanted in to the armory.

I mainly wanted to get Preston out of SH and now I plan on moving the rest aside from Momma Murphy and Codsworth. Now I can.

But yeah I'm nervous about that area now. I have no idea if the quest will re-trigger.

I did take the castle twice before on different characters without this issue. One was with the MM and one on my own. But like you say, the egg nests do not clean up.