Hi, Chuck. I don't know if we talked about your question here.  Here is my take on it: The two sentences could be synonymous, OR they could refer to different events (or to different sub-events of the same big event), though in actual usage, this distinction might not be apparent to many speakers.
 
1. "Would you mind if I added your name to the list?"
Yes, this -ed ending follows the rules. The question refers to a hypothetical completed action: the state of the name having been added to the list. Hence the -ed ending.  So the speaker is asking the hearer if she would mind a state or condition in which her name had been added to the list by the speaker.
 
It seems to me that the second example has a slightly different meaning in that it refers to the beginning of the speaker's action, but not its completion.  I don't know how aware speakers might be of these distinctions if, in fact, they exist.
 
2. "Would you mind if I add your name to the list?"
 
This question refers to a hypothetical act of the speaker taking a pen and beginning to write the name on the list.  She is asking if the hearer would mind this undertaking.  While sentence 1 refers to the completed state of the name being on the list, sentence 2 refers to the act of the speaker actually writing the name on the list.
 
You can imagine different situations in which these distinctions might be important. For example: 
Would you mind if add your name to the list, or do you want to do it? 
*Would you mind if I added your name to the list, or would you want to have done it?
 
Linda 
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