Verifica el formato de la fecha y el tipo de columna de la tabla.
El hecho de que te almacene esa fecha sugiere que no el campo es un UNIXTIMESTAMP, y que no le est´qa llegando el dato.
Cita: A DATETIME or TIMESTAMP value can include a trailing fractional seconds part in up to microseconds (6 digits) precision. In particular, as of MySQL 5.6.4, any fractional part in a value inserted into a DATETIME or TIMESTAMP column is stored rather than discarded. With the fractional part included, the format for these values is 'YYYY-MM-DD HH:MM:SS[.fraction]', the range for DATETIME values is '1000-01-01 00:00:00.000000' to '9999-12-31 23:59:59.999999', and the range for TIMESTAMP values is '1970-01-01 00:00:01.000000' to '2038-01-19 03:14:07.999999'. The fractional part should always be separated from the rest of the time by a decimal point; no other fractional seconds delimiter is recognized.
Claro que sin código solo podemos adivinar...