This is an issue that's related to the css-property overflow. I think you could change the overflow of the contentpane. If you know what you're doing in CSS :)
Edit: If you set the overflow to hidden, it may be that not the hole pane is showed. So if your page is longer than the pane, it will be difficult to scroll to the downside.
Thanks to Marcel Vuijk:
In Mendix 2.5.0 the file reset.css was loaded on all elements (h1, h2, h3 elements etc.) which took away the margin. In 2.5.1 this file will no longer be generated. This is already known and will (hopefully as soon as possible), solved from the modeler. But for now it must still be solved with the theming, which is as follows:
In the theming stylesheet (custom.css): . Tundra. MendixFormTitleborderLeft. MendixFormTitleborderCenter. MendixFormTitle_title ( / / Here are some style attributes. )
Add attribute "margin: 0px! Important,"