Text of the email does not wrap the window down

By opening a received e-mail (double click) the long lines of text are automatically wrapped without using the scroll bar.
If you expand the mail window to full screen, when you return to reduced display the text is no longer automatically wrapped, but you have to use the scroll bar to read the whole mail.

Steps to reproduce:

• import the attached email
• open the email with double click
• the text of the email is shown all without having to use the horizontal scroll bar (text wrapping automatically)
• expand the window to full screen
• reduce the window to the initial size again

Expected behaviour:

• the text of the mail is shown all without having to use the horizontal scroll bar (text wrapping automatically)

Actual behaviour:

• to read the text, use the horizontal scroll bar