M5Stackで整数20200211をfloatの変数に代入すると20200212になってしまう

float_20200211.ino

#include <M5Stack.h>

float gps_date = 0;

// the setup routine runs once when M5Stack starts up
void setup(){

  // Initialize the M5Stack object
  M5.begin();

  /*
    Power chip connected to gpio21, gpio22, I2C device
    Set battery charging voltage and current
    If used battery, please call this function in your project
  */    
  // LCD display
  M5.Lcd.print("Hello World");


  gps_date = 20200210;
  Serial.print("gps_date = 20200210; // ");
  Serial.println(gps_date);
  gps_date += 1.0;
  Serial.print("gps_date += 1.0; // ");
  Serial.println(gps_date);

  gps_date = 20200211;
  Serial.print("gps_date = 20200211; // ");
  Serial.println(gps_date);
  gps_date -= 1.0;
  Serial.print("gps_date -= 1.0; // ");
  Serial.println(gps_date);

  gps_date = 20200212;
  Serial.print("gps_date = 20200212; // ");
  Serial.println(gps_date);

  gps_date = 20200211.1;
  Serial.print("gps_date = 20200211.1; // ");
  Serial.println(gps_date);

  double dv = 20200211;
  gps_date = dv;
  Serial.print("double dv = 20200211; gps_date = dv; // ");
  Serial.println(gps_date);
}

// the loop routine runs over and over again forever
void loop() {

}

result

gps_date = 20200210; // 20200210.00
gps_date += 1.0; // 20200212.00
gps_date = 20200211; // 20200212.00
gps_date -= 1.0; // 20200212.00
gps_date = 20200212; // 20200212.00
gps_date = 20200211.1; // 20200212.00
double dv = 20200211; gps_date = dv; // 20200212.00

1を足したり引いたりしてもダメで、一旦doubleに代入してからgps_dateに代入でもダメ。
gps_dateをdoubleで宣言した場合は問題ない。

結局floatの有効桁数不足という事でバグではありませんでした。orz