User detail issue

Hi i need help to solve an issue with user detail 's app

Problem : when a new user subscribe to my site, it automatically fill the field value with informations from another user!

Step to replicate : go to the website and subscribe as free user

Additional informations : the form refers to some content like this
<field name = "Nom" type = "text" size = "30" label = "COM_PAYPLANS_AC_USERDETAILS_FULLNAME" class="required validate-username" />
Where "COM_PAYPLANS_AC_USERDETAILS_FULLNAME" is related to content in language override files
Up to now it work well. But now it return wrong values.

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