Ok, so i changed out the block of my floyd and intonated and all that fun stuff but i've always had this problem that even with the strings locked at the nut its like my low E goes flat ! Very seldom does it happen with any other string (Besides the high E, i max the fine tuners out on that one quite abit) and i was wondering if its:
A) an easy fix like i just need to replace the nuts at the head stock or something
B) a tuning thing i'm missing (the strings are older so I know they are stretched)
c) i'm retarded

Hope someone can help me out soon! it sounds fantastic (especially after i put in a titanium block into it) when its in tune and intonated so i'm dying to get it going!
seriouslt though, i blocked mine for a long time and it did the same thing but with all the strings. after i fixed it up and got it working right, probably a solid 45 minutes of work, it doesnt do it anymore.
My sig? Nice.
If it's just the Low E, pluck the string and press on it behind the nut. If it changes pitch, than your nut is slipping and it's A).
You can call me Aaron.

Out on parole, any more instances of plum text and I get put back in...
I'd say it's possible that either your nut isn't locked properly/worn so that it doesn't lock properly or perhaps the string is slipping in the saddle. When I got my latest guitar the tuning was in B standard and it was horribly unreliable, a setup by me and a new pack of strings later it's in D standard and working great, part of the problem was how short the guy had cut the strings and positioned them in the bridge, they were slipping.
My Gear:
Suzuki Classical Guitar from 60s
B.C. Rich Warlock
Epiphone Les Paul Junior
Monterey Steel String Acoustic
Maton M255 Steel String Acoustic
Agile AL-3100 w/ EMG 81/85
Bugera 6262-212