MSBuild a .dbproj seems to run twice - msbuild

Question

When we build our Visual Studio 2010 Database Project from the command line using msbuild.exe it can sometimes run twice from the same command line.
We call msbuild from a nAnt script, and just call the 'Build' target. Our database project is quite large so it can take about 4 mins to run through a single time. When it runs through twice our database build takes over 8 minutes.
Here is the exec section we use to call the build. It runs on a .sln file that only has a single .dbproj in it.
<exec program="${framework::get-tool-path('msbuild.exe')}" append="true" failonerror="true" verbose="true">
<arg value="${database.sln}" />
<arg value="/p:OutputPath=${build.output.database}" />
<arg value="/nologo" />
<arg value="/t:Build" />
<arg value="/p:Configuration=Release" />
<arg value="/p:WorkingDir="."" />
<arg value="/verbosity:normal" />
<arg value="/v:m" />
</exec>
The output we get looks like
Creating a model to represent the project...
Loading project references...
Loading project files...
Building the project model and resolving object interdependencies...
Validating the project model...
(x) problems have been detected.
[a list of warnings based on the db analysis]
The results are saved in (y).
Creating a model to represent the project...
Loading project references...
Loading project files...
Building the project model and resolving object interdependencies...
Validating the project model...
(x) problems have been detected.
[a list of warnings based on the db analysis]
The results are saved in (y).
Can anyone help as to why the target seems to be called twice (only sometimes - I haven't figured out why only sometimes). The script always runs on an empty folder structure so there is never a build output left over from a previous run of the build.

Answer 1

First of all try to change the output verbosity to diagnostic for MSBuild:
<arg value="/v:diag" />
And the same for the Ant script. I don't have experience with Ant , but you shpould know how to do it ;)
Hopefully you will find a reason in the diagnostic logs...
BTW:
You have duplicate command line options for MSBuild. Remove one arg from the following:
<arg value="/verbosity:normal" />
<arg value="/v:m" />
/v is abbreviation for /verbosity see MSDN for MSBuild command line options reference.