I recently installed OS 10.8, and now my mail and calendar accounts want to default to my sister and her email address?

Question

Here is my situation:
My sister and I have shared an Apple ID ever since I bought my sister an iPhone on my cell phone account. We each have Mac laptops and had no problem syncing to separate Gmail/Exchange accounts but still share an Apple ID for convenience.
However, after I installed Mountain Lion, the account settings in Systems Preferences will default to having my sister's name instead of mine. I would change the name to my own, enter my own Gmail and Exchange accounts and everything will appear okay, but then, when I come back, the name automatically reverts to my sister's! (The email address and other account information remains my own though.)
If this were the only issue, I would be able to deal with it, but the most bothersome aspect is when I try to make an appointment in Calendar and set an alert email to myself, the only options are my SISTER's email addresses. I don't even have an option to change it. When I was running 10.6.8, the email address options were my own address.
I am flummoxed as to where my computer is getting my sister's name and email address. I went into my Apple ID account and no where does it list my sister's name or email address. How do I remedy this?
Thanks in advance,
Tuan
***I figured it out by the answers that popped up after I posted.  Apparent this is a frequent problem. Somehow, my sister was assigned as "Me" in Contacts after the install (I still don't know how.) But after I changed me to me, the alert email address were mine.

Answer 1

Here is my situation:
My sister and I have shared an Apple ID ever since I bought my sister an iPhone on my cell phone account. We each have Mac laptops and had no problem syncing to separate Gmail/Exchange accounts but still share an Apple ID for convenience.
However, after I installed Mountain Lion, the account settings in Systems Preferences will default to having my sister's name instead of mine. I would change the name to my own, enter my own Gmail and Exchange accounts and everything will appear okay, but then, when I come back, the name automatically reverts to my sister's! (The email address and other account information remains my own though.)
If this were the only issue, I would be able to deal with it, but the most bothersome aspect is when I try to make an appointment in Calendar and set an alert email to myself, the only options are my SISTER's email addresses. I don't even have an option to change it. When I was running 10.6.8, the email address options were my own address.
I am flummoxed as to where my computer is getting my sister's name and email address. I went into my Apple ID account and no where does it list my sister's name or email address. How do I remedy this?
Thanks in advance,
Tuan
***I figured it out by the answers that popped up after I posted.  Apparent this is a frequent problem. Somehow, my sister was assigned as "Me" in Contacts after the install (I still don't know how.) But after I changed me to me, the alert email address were mine.