I figured out the problem!
picarto seems to have lately added the HTML5(MP4) playback option for its player, which doesn´t seem to work for Opera. The thing is that it´s set as the default playback option and once the stream is fully loaded, the menu for changing to another playback format simply disappears.
This means that you CAN watch streams as long as you´re fast enough at the beginning to switch to Flash or HTML(HLS) before the stream itself is fully loaded in HTML5(MP4).
Picarto takes the blame here as it seems