In the present case, it should read, custruitu à u seculu XII (built in the 12th century). The error relates to the disambiguation of French ‘construit’. It can translate into:

• custruitu (built): past participe, masculine, singular
• custruisce (builds): present simple, third person

MT should (i) find the proper reference of ‘construit’, i.e. ‘clocher’ (church tower), but above all (ii) whether  ‘construit’ is a past participe or a present simple. Some kind of dependency parser is in order…