When the user leaves a data block of records and comes back to it, position the user's cursor where

I know this is probably a very simple thing to do, but I have not been able to figure out how to do it...

Anyways, I am using a master-detail relationship to link to data blocks together on one form that are actually 2 separate tabs. When the user chooses a record on the first tab ("master" block) and then clicks on the second tab ("detail" block), it works correctly and puts the user's cursor at the beginning of the block for that specific "detail" record(s) that pertain to the "master" record that the user has chosen. But, when the user clicks back on the first tab to go back to the "master" block, it automatically goes back to the first record of the block.