When viewing a code file in the source browser the windows its content is displayed is too small when viewing it on a smaller (e.g. 1024*600) screen, hence its height is determined proportionally with the screen height, without a minimum height. That's even worse if the file is in a diff view. See e.g.: http://orchard.codeplex.com/SourceControl/changeset/changes/d455771c1974#src%2fOrchard%2fEnvironment%2fExtensions%2fCompilers%2fCSharpExtensionBuildProviderShim.cs
On my netbook's screen here I see five rows from the source file.
This could be simply solved by adding a min-height to the window, I would suggest ca. 500px.