Variation in fonts with composing email

I am using the free version of eMClient, version 7.1.33101.0, on Windows 8.1
I have set my default settings to use Calibri, 12 , black font.

However, I noticed a problem.

When composing multiple line email, the font type, size varies. Atleast two varieties.  I have a personalized HTML email signature also set up to compose. So does that make a different.

I suppose if your cursor moves from the body text are to the signature area, then the font might change.

Maybe compose and send me a message from eM Client that shows this. My address is gary@gmx.se