Numberformatexception error

When someone sends me an email with large attachment (more than 10MB), K9 not only blocks this mail (under Inbox i see Numberformatexception error), but also blocks all the following mails. I’ve found out that if I change Fetching size option from default (32 kb) to Download complete message, the problem disappears. But I don’t want to download the large messages automatically. What is the point of Fetching option if it doesn’t work the proper way?

This problem appears with mail.ru emails. It seems they changed something on their servers and now you can’t receive mails with large attachments if you don’t change fetching size to Download complete message.
Is there any way to change something in K9 settings (fetching size rules?)?

The problem is gone. I guess mail.ru fixed it, since it resolved by itself.