Why will the control Not come out of Silk Test after invoking an Application exe with Sys_execute() function

Find the Functionality of SYS_Execute below.

1) Do not use SYS_Execute to execute .reg files; use the Start command instead. SYS_Execute was designed to execute commands that do not require user input and that terminate almost immediately after  it has been executed. SilkTest waits for any command that brings up a process requiring user input.
 
For example: SYS_Execute  ("freecell.exe") starts Freecell in an invisible window and SilkTest  does not continue until the Freecell process is terminated. On the other hand, SYS_Execute("start freecell.exe") starts Freecell in a visible window, and still SilkTest does not continue until the Freecell process is terminated.