Filtering on phone numbers with a + prefix

[dv8inpp]

I can filter on USERS_URL = 'http://192.168.1.231:8069/api/res.partner/?query={id, phone, name, company_id{name}}&filter=[["phone", "=", "12345678"]]'

but cant filter on USERS_URL = 'http://192.168.1.231:8069/api/res.partner/?query={id, phone, name, company_id{name}}&filter=[["phone", "=", "+12345678"]]'

Is this a bug or misuse of the filter function