Hello,
One interface connected to the USB is used to display some trace on my terminal.
The other Hardware Uart is used to communicate with another device.
And sorry for not showing my code, but unfortunately I am not allowed to show it... but anyway it is quiet large so I do not think it could help... Maybe I post to the wrong section of the forum! 
I will have a look to check all the array writing to avoid memory corruption!
Thank you