I'm not sure how long this has been happening, but it appears Google is treating sub-domains differently on their international engines.  I'm specifically referring to sub-domains used for an foreign language site.  Several big brands utilize this structure, especially for Spanish versions of their websites.  For example:

www.Espanol.Marriott.com
www.Espanol.Vonage.com
www.Espanol.Aflac.com
www.Espanol.Wunderground.com

All of these big sites utilize a sub-domain for their spanish versions, as ccTLD's such as .com.mx, .com.co, .es, and ALL of the other Latin American/Spain TLD's would make for a very large number of websites to individually maintain.  While there are significant benefits to roll-up a language as a sub-domain, there are negative aspects for SEO, as Google likes to rank content for a domain that matches that version of Google. For example Google weighs .co.uk content more favorably for searches on Google.co.uk naturally, as it's content speaking to a UK searcher.

So this brings me to my point...even though Espanol.Domain.com is not using a ccTLD, Google has been pretty good to date ranking Spanish language content on the Latin American Google's of the world.....but not anymore.

It appears Google has taken a step back, and is now devaluing Spanish sub-domains, instead preferring to display the English, Domain.com version, even on core branded searches.  Even more egregious, Google is now displaying the Espanol versions of these sites - content in Spanish, more relevant to a searcher in Latin America mind you - as a Site Link underneath the English site!

Let's look at some examples:

Keyword: [vonage]

Keyword: [wunderground]

Keyword: [aflac]

Keyword: [marriott]

Not sure why Google has decided this is more useful or relevant for Spanish users.  Let's hope this is just a test, and Spanish content once again ranks prominently in Spanish language search engines (at least above the English domain on default searches). 

If not, give webmasters that option, because this current scenario doesn't make a whole lot of sense.