When you subscribe to a tag you get mail about new questions for that tag. If you yourself write a question with a tag you are subscribed to this question will be included in mail updates about that tag. This seems unnecessary since you already know about questions you have written yourself. It is not that bad if you get mail updates about a tag where your question is one of several but it is annoying for tags with less traffic where it can happen that you get mail updates for a tag where your question is the only listed one.
I suggest to either simply not include own questions for in mails from subscribed tags or to provide an option to not include them.