Why ITA Matrix is failing so much last months?

Last months I've noted that Google ITA Matrix is giving results (ticket prices) impossible to buy. The first time I perceived it, I was going mad to find where to book this ticket price online and after a lot unsuccessful search in sites like Edreams, Trabber... I tried to book it through a physical travel agent without success (I asked in two different agencies).

An example of today. If I search a flight from Cancun to Madrid using ITA, something like this:

I get this result:

But when I try to find a price similar to the showed in ITA using an online tool, it's impossible to find any similar price, even the company site gives prices near the double.

What's happening with this? It's not a problem with a given company, but I've found that there are airlines that are more given to return inexact prices (i.e. is common that Turkish Airlines gives prices lower in ITA than in other search engines).

Is possible that some companies are giving fake prices to ITA? Or is ITA who is not searching right? Or may be the problem is that I don't know how to find these prices than ITA can?

NOTE: I've tried to use proxy servers to avoid the location problem. In the example given above, I've used a Mexican proxy to pretend to be in Mexico without success.