Update: Problem solved. There was a problem with Imgur hosting images for visual styles, migrated all the images (80 of them... doh) to TinyPic.
Also Chrome changed the way it interprets filter drop-shadow on buttons.
Sorry, it hasn't nothing to do with Stylish.
From the last update a lot of the users of my style are complaining. Most of the images don't load. At first I thought it was Imgur that made recent changes, but some images hosted there load correctly. After that I noticed that a lot of shadows disappeared also, so Imgur discarded, has to be Chrome or Stylish. And it only happens in Chrome.