Why does F# compiler generates IL NOP even in release builds?

I've just stumbled across this and I'm a bit puzzled.

I have an out-of-the-box VS 2010 F# project, with all default settings, targeting .NET 4.0.

The F# code is like this:

let test(a:int, b:int, c:int) = min a (min b c)

When I compile it for release, the generated IL contains some strange NOP instructions scattered around. Like this:

The generated IL for this (with all default settings):

.method public static int32  test(int32 a,
                                  int32 b,
                                  int32 c) cil managed
{
  // Code size       20 (0x14)
  .maxstack  4
  .locals init ([0] int32 V_0)

  // HERE
  IL_0000:  nop

  IL_0001:  ldarg.1
  IL_0002:  ldarg.2
  IL_0003:  bge.s      IL_0009
  IL_0005:  ldarg.1

  // HERE
  IL_0006:  nop

  IL_0007:  br.s       IL_000b
  IL_0009:  ldarg.2

  // HERE
  IL_000a:  nop

  IL_000b:  stloc.0
  IL_000c:  ldarg.0
  IL_000d:  ldloc.0
  IL_000e:  bge.s      IL_0012
  IL_0010:  ldarg.0
  IL_0011:  ret
  IL_0012:  ldloc.0
  IL_0013:  ret
} // end of method Module1::test

My .fsproj project configuration is:

  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
    <DebugType>pdbonly</DebugType>
    <Optimize>true</Optimize>
    <Tailcalls>true</Tailcalls>
    <OutputPath>bin\Release\</OutputPath>
    <DefineConstants>TRACE</DefineConstants>
    <WarningLevel>3</WarningLevel>
    <DocumentationFile>bin\Release\TestFsIL.XML</DocumentationFile>
  </PropertyGroup>

Now, if I comment out line <DebugType>pdbonly</DebugType>, the NOP instructions disappear. But of course so does the PDB file!

.method public static int32  test(int32 a,
                                  int32 b,