After i save message by selecting removing encryption, email cannot be opened an show with blue lock

Hi, 

I receive S/MIME encrypted email. I must upload email to document system and remove encryption.

I go message properties and under security unselect Encryption. Then select save I get popup that encryption will be removed. Click yes and process is ok.. Sometimes happens, that after save I get an error.

Padlock change from whit to blue. And I can not open it.

I have now started to do a copy of email and try to remove encryption. If process fails, I  use backup copy to repeat the process and process is successful.

Is there a bug or an issue, in outlook.  It not always, but I never know, when this issue will appeared and it is annoying.