Welcome to the site!! 
If I'm understanding your question correctly I believe what is happening is after you downshift in automatic, you are going to have to upshift in auto as well, unless you do not use the paddle shifters for (I believe) 10-15 seconds.
Lets say your going down a hill in auto and you downshift to 4th, if you go uphill or level off, your going to have to upshift using the paddle shifters unless a span of 10-15 seconds (I believe this is correct, FlipSide can help me with the correct timing) has elapsed since you last downshifted into 4th. It happens to me a lot, I, like you, like to downshift in auto mode (when its used) and then continue to drive but unless I switch to manual and then back to auto or wait a certain period of time before pressing the paddles again, it doesn't reset and I will redline it or have to use the paddles to upshift.
Basically I believe there is a certain amount of time you have, when in auto, that if you use the paddle shifters, your going to have to wait until the computer puts you back in auto and will do all the shifts for you
I'm not sure if I'm making myself clear or not, perhaps someone can clarify it for him
If I'm understanding your question correctly I believe what is happening is after you downshift in automatic, you are going to have to upshift in auto as well, unless you do not use the paddle shifters for (I believe) 10-15 seconds.
Lets say your going down a hill in auto and you downshift to 4th, if you go uphill or level off, your going to have to upshift using the paddle shifters unless a span of 10-15 seconds (I believe this is correct, FlipSide can help me with the correct timing) has elapsed since you last downshifted into 4th. It happens to me a lot, I, like you, like to downshift in auto mode (when its used) and then continue to drive but unless I switch to manual and then back to auto or wait a certain period of time before pressing the paddles again, it doesn't reset and I will redline it or have to use the paddles to upshift.
Basically I believe there is a certain amount of time you have, when in auto, that if you use the paddle shifters, your going to have to wait until the computer puts you back in auto and will do all the shifts for you
I'm not sure if I'm making myself clear or not, perhaps someone can clarify it for him