Glyphicons return wrong symbols or errors / Thumbnails display only text / Buttons don't display gradients

Created by: ghost

There seems to be a problem with glyphicon.less (wrong or no sysmbols), thumbnails.less (displays only text) and the button gradient, which is not displaying at all.

I am using Bower to pull the latest LESS version of Bootstrap and compile CSS/JS with Grunt:

{
  "name": "bootstrap-grunt-bower",
  "version": "0.0.1",
  "dependencies": {
    "bootstrap": "latest"
  }
}

I am organising my main less-file as suggested. In order to test the setup I am using the sample Bootstrap theme. All features display correctly with the mentioned exception.

Would appreciate your advice.