When you have two open drawings and one person saves, a message should pop up Reload Electrical Project Database. It is important to do this. Also when opening a connected drawing a message will pop up and there is a check box to remove the data from the epd. Make sure it is not checked. Otherwise if it is, it might remove the information in the other drawing.
Make sure the epd is set to relative path if you are moving the drawings around. If you are taking it home, only one person can do this. They have to take the epd file and the one you are working on. Copy both back into the directory and then you will get the Reload message.
Do not rename a drawing attached to the epd. Use saveas and then open the drawing you do not want and disconnect the epd from it.