If you sign and encrypt a mail , after decryption two or more blanks in sequence blank's are replaced by  plus a blank character.
For example:
Karl Heinz Weg 12
becomes
Karl Heinz Weg 12
I recognised that problem during a test of Gpg4win, where my outlook signature was not correctly transferred via an encrypted and signed email. It only happens if you have two or more blanks in sequence.
The same behaviour also happened if you put the same text into the body of the email.
We it could reproduce the problem on two different computers.
The setup of my computer is a Windows professional 10 64 bit system with an actual patch status with a Outlook 2016 and Gpg4win 3.0.0. The Outlook 2016 message format option was set to HTML. If you changes to rich text or plain text there is no replacement of the blanks .