Strings get repeated when over 255 chars

I've noticed that all my strings over 255 got repeated each time I've clicked on "Scan for messages" - https://github.com/rainlab/translate-plugin/issues/27
Checking the "code" field on DB I've noticed that it's VARCHAR 255, so limiting the code to those 255 chars solved the issue and it doesn't repeat string anymore.
I thought on changing the field type on the DB but I think it makes no sense having codes that big, right?