Some of the Applications are getting downloaded more than once from Android Market
I myself got to know why its happening. 
First I selected any application from the Android Market and say Install and then Ok. Its going to start Downloading. 

I observed this in two scenarios. Both of the cases are pretty much same.

Case I.
If I Minimize/Kill the Android Market application while Downloading using the Back Button then it completes the Download and Starts the new Download again.

Case II.
I Minimize/Kill the Android application while Downloading using the Back Button and again open the Android Market application, then we can see the same application is getting Downloaded twice from the Market. If we do the same thing again then we can see the application is getting download more than thrice.

The solution is Simple. If any application is getting downloading from the Android Market just press the Home key to minimize the Android Market.