QR codes turning into negative

Hello Folks,

                   I am new to corelDRAW, and we have shotly adopted CorelDRAW 2018 mainly for the purpose of drafting user manuals.

Error description:

We use QR codes saved and PNG files saved to our local drive. So when we import this file to the document, it is automatically converted into negative. 

I know one solution is to use "Transform" feature under "Effects" tab. But it would be really helpful if someone could guide me to prevent automatic conversion of PNG file into negative file.

Waiting for your precious ideas,

Thanking you