Cannot Read S/MIME Encrypted Mails On IPhone 5s And IPad

I have a Certificate for my email address by Comodo. It is installed in Thunderbird on PC and iPhone and iPad with iOS 7.1.2.

Thunderbird on PC behaves like expected, i can send and read encrypted emails.

On iPad and iPhone i cannot read encrypted emails.

I imported my S/MIME Certificate via email attachment (p.12-File) and activated it in the mail section for my account. I also enabled signature and encryption function.Â

1. When i receive an email that is signed but not encrypted, the certificate of the sender is trusted & installed.

2. When i receive an email that is encrypted, the same sender is now shown in red color. I cannot read the email, because my profile allegedly does not contain my identitiy.

3. When i try to reply to the signed but not encrypted email (1.) then the message i send is signed but not encrypted, even though the address is shown in blue with a lock (which text info: encryption is possible).

4. When I send an encrypted email to my own account via ipad or iphone, i can read it on both ipad and iphone. This makes me think that the iOS Mail App uses S/MIME encryption a little bit different then Thunderbird.Â

All of this does not fit together. It think I correctly installed my certificate but there are problems in the Mail Program on iOS.

Info:
iPhone 5s, iOS 7.1.2, also applies to iPad Mini iOS 7.1.2