Hi Aurelio!
I suspect this may be a peculiarity of your theme. A quick way to test this theory would be to switch to a default theme like Twenty Twelve and check to see if the title tags are populated. Assuming that’s the case it may be worth touching base with the theme author and asking about how the title tag is populated (does it use wp_title() and does the theme apply any wp_title filters of its own that might be tripping things up here?).
If changing the theme doesn’t help just let me know – the next thing to look at at that point of course would be your stack of plugins, with SEO-type plugins being obvious candidates to try deactivating in the first instance.
Hope that helps!