Docking Port Glitch - Help Debugging Persistent File?

[Srpadget]

I have a "reusable" deep space tug (it's one of my standard designs, I've got several of them scattered around the system and they've been successfully hauling things for some time now) that delivered a Jumbo tank of LF/O to an orbiting space station (the tank and station are also standard designs, used successfully yadda yadda yadda).

And now I can't undock the tug from the delivered Jumbo tank. I get the "Undock" option on one docking port, as usual...but when I click it, nothing happens. Ports/vehicles don't undock, viewpoint doesn't change to the new CoM of either vehicle, and for that matter the "Undock" command doesn't vanish. It's like nothing got clicked.

Docking surfaces are Clamp-o-Tron Sr's, which I docked in LKO (and as mentioned earlier, they're bog-standard designs I've used successfully before), so I know neither of the ports are installed backward.

I have tried quitting out of KSP completely and restarting. No joy.

I am currently assuming that the state of at least one of the relevant docking ports has gotten corrupted in the persistent file. However, I'm not sure what I should be looking for or what I should change to fix it. (Plus, of course, the station has 6 Clamp-o-Tron Sr's, 2 of which are currently occupied by detachable tanks for a total of 4 more C-o-T Sr's, and the tug of course has one for a total of 11 large docking ports on that composite "craft" in the persistent file.)

So can any of you persistent-editing experts tell me what a "healthy" docking port should look like, and how to spot (and fix!) the "problem child" in that morass of docking ports?

Edited September 26, 2015 by Srpadget
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[Snark]

I've never delved into docking ports per se (since I've never had a bug like that), but a couple of suggestions:

Craft files store parts as a tree, and each "parent" part has references by ID to the child parts. Therefore, if you can get a "toehold" by finding some part somewhere that you can recognize (e.g. suppose you know a particular kerbal happens to be in a crew cabin on your space station-- you can locate that part by searching for the kerbal's name), then you can see what links to it and "follow the chain" until you get to the one you want. Really tedious and unpleasant, but once you crack open the .sfs you're asking for it.

It should be pretty straightforward to see what a "healthy" pair of docking ports looks like-- just find some other docked pair on some other ship somewhere, where there are only two ports involved, and you can use those for comparison once you find the borked ones.

[Srpadget]

Well, well, well... that turned out to be LOTS easier to fix than I thought it would.

I didn't have to crack open the .sfs at all.

It occurred to me that it'd be a lot easier to troubleshoot if it was a much smaller craft with fewer ports (and fewer parts generally). So I undocked the tug-and-tank combo from the station. Then I decided to try undocking the tank one last time, just on the off chance that the problem fixed itself when the craft was split in two and the part trees rebuilt themselves.

Pulled about 20 meters away from the station, hit Undock, et la voila--We Have Separation!

And then, well, I might as well go for broke, right? Redocked to the tank, headed back to the station, redocked to that, and then SUCCESSFULLY undocked the tug from the tank. And now the tug is headed back to Kerbin with a load of returning crew and a mound of tasty Science.

The whole thing took maybe 10 minutes and a few units of monoprop. (And did NOT involve trying to debug someone else's data structures, yay!)

I call that a win.

[The_Rocketeer]

I call it a bug.

Still, grats!