I did a little research into your issue and found what is causing it and a workaround for you.
The SortTable command is trying to append the rows to the table. The table is being determinded by the row you specify in the command, and then up one level. In your case, the table becomes my:myFields.
When the rows are sorted, they are appended into the table. This is where the problem occurs because your rows are NOT the bottom-most nodes of the DOM. The command currently is not able to put the rows back into the middle of the DOM tree (which is where they are currently located). This is an issue we have logged and will look at fixing in a future release.
In the meantime, there are two workarounds:
1. Move your repeating table into a container group. This is the best option as it componentizes your table and the structure has some advantages in InfoPath. The new structure would look like:
my:myFields/my:Accomplishments/my:Accomplishment
where Accomplishments is a group and Accomplishment is the individual repeating row.
2. Locate your table at the end of your schema. This is not a good option because your schema might later change and you would have to always ensure it stays at the end. Plus if you ever have another table to sort, you run into the same issue for that one.
We encourage you to choose workaround 1 above as it follows best practices for schema design.