Feedback from buyer disappeared

I sold to a buyer with 0 feedback.  At first I was hesitant but the buyer paid and I shipped the item.  They confirmed they received the item and left me positive feedback so I did the same.  Everything was good for awhile until I logged on today and noticed that the feedback they left me had disappeared but the feedback I left them is still there.  They are still registered user so I don't know why this has happened.  Should I be worried? 

It may be that eBay removed the feedback due to the dsr star rating the buyer left you or it mat be the buyer breached feedback policy in a way only understood by ebay bots or reps.

I would not be concerned, but thats just me - if you are worried or just want more info IMO give eBay a call and enquire directly

I was worried so I actually contacted ebay through email. They responded 2 days later saying they needed more info which I did provide them. After that, I did not hear from them for a whole week so decided to follow up once again and still nothing. No responses at all from ebay. I checked the buyer's feedback and they still have 1 postive feedback which I left them. Not sure what to do now. Should I be concerned at all.