Disappearing reactors?

Hopefully I'm not the only one who has had this, and if I am missing something written about it, I do apologize.

My reactor keeps disappearing from inside my nuclear fluid reactor. The pressure vessel remains intact, and I see no evidence of a massive meltdown, however I try to access the hatch and get nothing, then open the reactor and find it empty. This has happened a number of times... I'm at the point where I just NEI everything back so I stop dumping in resources. Anyone else having this?

I DO have it build just over a chunk border, but it was happening at my old base before a big remodel and that one was within chunk borders I think.

Only major mods I'm running (that I was running before when this started) is Gregtech, AE, and Railcraft. There are other small mods but I don't think they'd be involved.
Anyone know what it is? Am I melting down and just not going Hiroshima? I have watched it alot and I see no problems, but I then come back to find it totally disappeared.

OK, and for another oddity, I keep having the oddest issues with disappearing/rotating blocks. Admittedly, I used worldedit to copy my coolant chiller design, and it was understandably all rotated incorrectly, however after fixing it, I saw that the original chiller had gone crazy. All mekanism pipes had disappeared, and so did the steam generators. Am I missing something obvious here, like it just being a reaction to a badly designed device and the steam generators blowing up (with no other damage)?

Figured it out! Reactor was melting down, just wasn't going Chernobyl on me, and the steam generators were exploding because I was losing water in the system. My bad! Ha!