RS232 port reading technics

Question

Hello,
I LOVE this forum. I (almost) always get the right answer from very good friends.
I hope the day will come when I can help others....still learning.
In my application I read RS232 port with arbitrary data streams.
Each message ends with double LF/NL "\r\n\r\n" which I use as my messae end label.

I first used the  msg = comPort.ReadExisting(); that I parsed programatically, but then I found out that I can let the prot do the work, and changed to:

msg = comPort.ReadTo("\r\n\r\n");

reading goes perfect, and I was happy until I found out that more often than not, when closing the port I get an error from the prot.

"The I/O operation has been aborted because of either a thread exit or an application request."

I assume it is due to incomplete reading of the message, which I don't really care about (I am closing the port, am I not?).
I can easily ignore the error by throughing an exception and returning from the catch, which works well, but, I am sure this is the wrong way to go.
Any good idea on how to make it right?
Thanks.