Galaxy Tab 7.1 - Email disappear from yahoo inbox

[AC Question]

I have Yahoo mail app in the device, I received the email, I tried to reply. while woking on the reply, the email disappear from the inbox, when I do a email search, I can see the email and indicating it's in my inbox, but I just can't find it in my inbox (I went thru all the folders).
When I went to my PC to check, the email is not in the inbox either. Worse, when I do a email search, it's not there either.
How can I restore the "lost" mail back to my inbox?