ipad mail app messing up my email - downloads items then removes them after I open a message.

My iPad mail app is messed up. It will download mail from my email server, show it in my inbox, then after I view an email it will remove everything when I close the message. All gone. Thankfully I have the ISP set so that the messages aren't removed from the server from this device. How is it that you make fixes to some things and they ruin others. I'm also having a calendar problem with ios 9 and it worked fine for several years.