I don't know if they've been spotted before, but oh well.
1) Artifacts: One game (mp), it automatically said "there's an artifact here" as soon as anyone colonized the planet with an artifact. Another time (sp), it automatically discovered the actual artifacts and gave them to you as soon as you colonized a planet containing one. Strangely, you could still explore the planet.
2) I scuttled some strikecraft being built by my Vasari Carriers. However, the actual strikecraft being build at the time were not scuttled. This led to me having some carriers with 3 sqauds. To tell he truth, I rather liked this bug. I can send you/post the RECORD file if you'd like.