I've been trying to restring my classical guitar Rafael Ortega R230. I've been playing guitar for a decade and have 2 electric guitars, one resonator, one western and the Ortega and yet this has never happened to me before. I could restring the EADgb strings without a problem. When I tried to restring the high e, I tried twice, once with a knot and once without (has worked plenty of times before). Enough context, here is what happened.

It took forever to wind up because it kept losing tension. Once I got it as high as b it lost tension so fast it barely got up to c until it dropped down to b again. I never got it higher than c. It just lost tension while I was winding it up. I looked all around. The knots near the bridge were tight, there was no wiggle room anywhere were the string could contract while you wind it up and lose tension. Everything was tight and looked normal. I tried two new strings, both clearly marked as high e and both clearly the thickness you'd expect from a high e. The tension wasn't very high when they were at b as well, so it really weren't accidentally b-strings. I kept going from b to c and back until both strings broke.

Now I really don't know what to try anymore. Everything looks normal. The strings were normal. I can't keep wasting high e-strings, but I haven't the faintest idea what is happening.
The gear maybe not screwed down tight causing the barrel to slip or it could be a mechanical failure in the barrel post but I don't understand the strings breaking at all. So check if the string itself is slipping on the barrel or the barrel is not turning correctly as you wind.
OTOH if strings are breaking they HAVE to be the wrong strings, right?
Pretty confusing.
usual suspects are:

-bad technique
-mechanical issues
-bad strings

post a picture of the tie block with the strings on. up-close and sharp.
Last edited by ad_works at Mar 25, 2016,
If your strings are properly secured at both ends, I would suspect a stripped plastic bushing on the tuner.

Mark the plastic bushing (the thing that the string wraps around) with a marker. Watch as you tune. If it stops turning at some point, there's your problem.
These tuners on classical guitars are usually quite simple to rebuild... You can probably get new bits from your shop's spare-parts bin, should that prove to be the problem.