Why are my spaces converted to tabs?

I have some text that contains whitespace at the beginning of several lines. When I copy it into the mail client the spaces are converted to tabs. Since I’m emailing code, the tabs are breaking my code.

How to reproduce. Sample text:


Copy this text into a new message. Unselect and reselect the text, or send the message to yourself and re-copy that text. The newly copied text will contain a tab and a space before “continuous” rather than two spaces. I also tried right-clicking and selecting “paste as text” but it didn’t change the behavior.

Is there anyway I can prevent this from happening?