Bold thread titles indicate that you have not viewed that thread online. Once you view the thread online the thread title is no longer displayed in bold for you.
Since you have always seen the threads that you have started, they never appear bold to you, but they will appear bold to everybody else until they have viewed the thread.
Also, by default, the system subscribes you for individual emails for any public replies to your post. So whereas the rest of threads may say "Daily Digest" in the subscriptions column (which speaks to how YOU receive notifications of future replies, other users will see this post according to there subscription level), threads that you have started or reply to will show "Individual Emails". For more info, see:
https://www.waccobb.net/forums/wacco...on-thread.html
and
https://www.waccobb.net/forums/wacco...ly-digest.html