Add a "sort column" to easily Sort and Un-Sort
When you sort your schedule and then move a symbol, you cannot undo the sort.  By creating a column that numbers your tasks, you can use that column to re-sort your schedule to appear as it did originally.  Milestones does have a Task Number SmartColumn that numbers tasks for you, but once you sort, the Task Numbers are re-assigned.  Here, we will manually number the tasks in order to create a "sort column."
1. Choose Insert | Column | Text. 
2. Move the column to any column position and name the column (here, "Sort").
3. Click the Text tool in the Toolbox.   
4. Click in the first column cell of the newly inserted column.
5. Enter "1" and then hit the down-arrow key on your keyboard.
6. Continue numbering until you reach the final task.
   
Use Excel for numbering, then copy-and-paste into Milestones
A very fast shortcut method for steps 3-6 is to use Excel to create the numbers, then copy and paste into the column.  This is especially helpful if you have a large amount of numbering to do.
1. Open an Excel spreadsheet.

2. Enter the first few numbers in a column, as shown on the right:
3. Highlight those numbers.
4. Click the lower-right corner of the highlighted block of cells, then drag down.
5. Release the mouse button when the desired number is reached.
6. The column of cells should still be highlighted; if not, highlight the column of cells that you just created.
7. Choose Edit | Copy.
8. In Milestones, highlight the column that will contain the numbering...  
9. Choose Edit | Paste Column Text.
Now, after you sort by Team, PM, Project, Date, etc., you can use the numbered Sort column to "retrieve" the original schedule.  To do this, use sort by selected column and choose "Numeric" when prompted.
You can hide the Sort column when not in use.  Right-click the column heading and choose Hide Column.  Right-click any column and choose Show Hidden Columns to display the hidden column.