Outlook.com attachments dissapear

If someone sends me an email with an attachment I can open and read the attachment. However, if I respond to that email (click "reply", then send an email back to the original email sender), the original attachment disappears. It's not that I can't open the attachment, it's just gone completely. No paperclip sign, no attachment at all - just gone. It is REALLY frustrating. Is there any settings I can change or anything I can do to make sure my attachments STAY in my inbox even if I reply to a message? I think the problem is that Outlook puts the messages together like a string of emails, and any emails that aren't the most recent lose their attachments. Can I make my messages stay separate and not turn into a string of emails? With my Outlook email at work I don't have this problem, only with my private Outlook.com email.