Having trouble using multiple exclusion attributes

I am using NCover 1.5.7 and trying to exclude 2 separate attributes from my coverage results. I'm using the NCoverExplorer custom MSBuild targets to call NCover from our build system. When specifying only one attribute to exclude it will work just fine, but when trying to you two it will exclude neither of them. I have tried specifying the attributes every different way I can think of but I'm wondering what I'm doing wrong here.

Here's my how I'm calling it in my MSBuild file:

<NCover ToolPath="$(NCoverToolsPath)"
          CommandLineExe="$(NUnitToolsPath)nunit-console.exe"
          CommandLineArgs="$(OutputPath)$(TargetFileName)
            /xml=$(NUnitMetricsBuildPath)$(MSBuildProjectName).xml"
          CoverageFile="$(NCoverMetricsBuildPath)$(MSBuildProjectName).xml"
          LogLevel="Verbose"
          LogFile="$(NCoverMetricsBuildPath)logs\$(MSBuildProjectName).log"
          WorkingDirectory="$(OutputPath)"
               ExcludeAttributes="NUnit.Framework.TestFixtureAttribute;Basis.Utilities.Testing.MockAttribute"
    Assemblies="$(OutputPath)$(TargetFileName)" />