Pan Preview message problem: my preview messages disappear when mouse go on

I have 2 email setted on my Thunderbird. I selected the option View=> folder=> unic (togheter, sorry I have italian version of Thunderbird). So I have two problem:

1) When I click on Inbox folder (for both profiles) nothing appears on preview pan, but some time if already selected one of profile and try to selecting inbox folder on the pan preview nothing change. (I continue to see the messages about the profile already selected). 2) In this case list of preview disappear when my mouse tough the message in preview pan. Ho can fix the problem? thank you Tony