I've used the TabContainer for a while now and up until my latest project, I've notced an inline style appearing on the body element that I hadn't seen before. Sure enough, I checked a previous project and it wasn't there.
<div id="ContentPlaceHolder1_TabContainer1_body" class="ajax__tab_body ajax__scroll_none" style="height:100%;display:block;">
I've removed it with jquery, but I'd prefer it not add an inline style at all.