Windows Live Mail ignores *certain* Emails

TLDR: Windows Live Mail does not fetch all mails from IMAP sent by IncrediMail.

Windows Live Mail (Version 2012 (Build 16.4.3505.0912)) seems to be ignoring certain emails from my Imap-Servers. I own a small webspace with a domain where I've got some IMAP-Mail-Accounts.

However out of about 3000 mails, six emails are ignored. They are nowhere, they are completly ignored. I have checked every single folder, the spam folder, marked them, marked them as unread, moved them to a different folder, added the sender to every list I could find, but Windows Live Mail still ignores them. There isn't even an error message.

The emails are correctly fetched by Outlook 2010, Outlook 2013, Mailbird, Inky, Thunderbird, the Webmail-Application and the Android MailApp. But no luck in Live...

As far as I know the mails were composed in "IncrediMail", if this helps. Since every other app displays them correctly, I would call this a bug in Windows Live Mail.

Is there any solution to this or a known bug with IncrediMail?

Thank You!

-Alex

If the Devs are interested I am willing to offer them the unfetched mails.