Wrong change to positive/negative temperature sensor values when going over zero

My temeprature sensor data is acting weird. When values goes thru zero, sign (positive/negative) of the value will change the opposite way, see graph:

My source data is ok, the sensor reads them from XML file. My config is like this:

- platform: scrape
    resource: http://192.168.1.250/xml.xml
    scan_interval: 300
    name: Teplota venku
    select: "temp_17"
    unit_of_measurement: "°C"