Strings on an ESP8266

Anyone know why this does not work?

if (field1!= "") {
MDCommand = "MD" + '\t' + field1;
Serial.println(MDCommand);
}

What I get on the serial monitor is:

Formatting MD Command:
inputstring: [795631813456 MEXICO 5/25/2019 A10012345
Delimiters: [|
Formatting MD Command:
field1: [MEXICO]
field2: [5/25/2019]
field3: [A10012345]

Following is the result of the Serial.println(MDCommand);

1: [MEXICO

Why does not display MD MEXICO?

field1 is defined as string field1;