Hello Pascal,
You must be referring to this issue on a particular field, such as the product, right?
By default on each model the name shown in the lists corresponds to the field 'name' in that model.
However there's the option to override this behaviour, in order to customize the name shown, by means of implementing method 'name_get' in a particular model.
In case of the model 'product', that is used in 'purchase.order.line', 'sale.order.line', '.account.invoice.line', the this method, as seen in the module 'product' and file 'product.py' does this concatenation:
name = '[%s] %s' % (code,name)
In order to avoid this you should create a new custom model, inherit from 'product' and redefine this method to suit your needs.
Regards,
Jordi Ballester
Eficent.