No bug here, all is working fine, but you probably misunderstand how Fireships work.
The basic strength (you can see this when training units) of the units shown in your first report is:
- Juggs: 1680
- Schoons: 900
- SotLs: 1440
- Redcoats: 100
So, with your first hit, you killed a total of
11*1680 + 1 * 900 + 28 * 1440 + 100 + x = 59800 + x = 4.746 * 12600 + x
The x here denotes whatever is missing from the report. I'm guessing some Bombs, Luggers, and Pirates, and I'm pretty sure they amount for about 5 * 12600 - 59800 = 3200 basic points (5 Fireships minus what I calculated above).
So, you killed approx. 5 * 12600 basic points, as expected.
As for the exp. gained, I don't know the exact formulae, but I do know that defending off gives far less than you'd expect. In normal hits, I it's 1/6th of the usual points, but FSs seem to give even less.
Next time when you find off out, send a raid and chart it. Also, I suggest you read this topic to gain more insight on how Fireships work.
P.S. I'm pretty sure that your second hit didn't kill all the units that were out.