It seems when you do the Escape from Oxbay/Speightstown quest where you capture a french ship, it is possible to retain both Rabel Yverneau and Tobias as officers. This happens when you capture 2 ships and assign them both as the captains. When you return to Redmond/Port Royale, you will appear in the governors office with Rabel and Tobias, they will walk out as usual and they are still captains of your captured ships. Not sure if this is a bug or by design, but it's a good way to get a lvl 12 officer witth a fair number of abilities fairly early in the game, as a plus he is a comrade in arms as opposed to a paid officer. The other bug I noticed is that some ships seem to not display a name or portrait. If these are in your fleet, it seems to cause a CTD at the world map.