UDP binding issue when items are updated

I have been struggling with errors on UDP binding.
My setup is quite simple : OpenHAB receives UDP frames containing ASCII values separated with commas (CSV), and I use a simple REGEX to sort out the channels required.
First setup was ok, but I noticed that when I update item file afterwards, I get errors like this one in the log:
[ERROR] [t.protocol.internal.UDPBinding] - transformation throws exception [transformation=null, response=24.0,22.9,21.4,28.0,30.2,16.3,99.9,17.0 NUL NUL NUL...

Please note that the text string is filled with NULL characters in the log (seems to be the 1024 bytes buffer), but I am not sure it is linked to the issue. I checked the communication with Wireshark and the UDP frame has the correct size.
I initially suspected that the updated item definition was wrong, or possibly a new REGEX (sometimes it was the case), but after many invesigations I found out that a fresh start of OpenHAB always runs fine, and UDP frames are processed correctly until I initiate an update of the item file.

Here is an example of one of the item defintion I use:
Number Temp_Room1 "Room 1 [%.1f °C]" {udp="<[*:'REGEX(.*,.*,(.*),.*,.*,.*,.*,.*,.*)']"}

This is very annoying since I have now to stop/start OpenHAB service each time I want to use a new item definition. I am wondering if there is an issue here with UDP binding.

Does that ring a bell to somebody ?

Thanks for help !