It seems that when updating an existing Contact via REST PUT, a supplied value for the Twitter social account will not replace a blank entry. PUT properly adds the Twitter account when creating a new Contact, but will not update an existing Contact.
Example data to use with REST PUT:
{
"duplicate_option": "Email",
"email_addresses": [
{
"email": "dolores.diva@example.com",
"field": "EMAIL1"
}
],
"family_name": "Diva",
"given_name": "Dolores",
"social_accounts": [
{
"name": "doloresdiva",
"type": "Twitter"
}
]
}