Contact Names Being Replaced

Probably happening because of dupe/mismatched email addys in your blast list.  If you upload a list w/email and names, and that email already exists in the database under another name, the record will update to the uploaded list's data if columns are not blocked from updating.
One way around is to only upload email addy column to static lists for blasts, it won't overwrite anything if there's no other data attached to that email.
Also, can block specific fields from updating in field management, I set them to not update from untrusted lists, and then lists coming from our (rather dupey, by email addys) customer database I upload as 'untrusted' so that names specifically do not update to match our in-house data, but stick with the de-duped and user-upated mkto lead record data.

Also, do you have the field Email Address available everytime your form is displayed? It is very possible that colleagues share your emails and when they do so write their names over the other person's name on form fill out. Unless it contains email address it won't create a new record.