Why Is It That Some FAKE Methods Don't Work Within Target Functions?

Consider the following:

#r @"FakeLib.dll"

open Fake
open Fake.StringHelper
open Fake.ProcessHelper

Shell.Exec("mkdir","exampleDirectory")

Target "DoStuff" ( fun () -> 
    trace "Doing Stuff..."
)

Target "Clean" ( fun () -> 
    trace  "Cleaning..."
)

Target "Deploy" (fun () -> 
    trace  "Deploying..."
)

"DoStuff"
    ==>"Clean"
    ==>"Deploy"

RunTargetOrDefault "Deploy"

The above script works fine, but when I move the Shell.Exec within a Target like this:

#r @"FakeLib.dll"

open Fake
open Fake.StringHelper
open Fake.ProcessHelper

Target "DoStuff" ( fun () -> 
    trace "Doing Stuff..."
    Shell.Exec("mkdir","exampleDirectory")
)

Target "Clean" ( fun () -> 
    trace  "Cleaning..."
)

Target "Deploy" (fun () -> 
    trace  "Deploying..."
)

"DoStuff"
    ==>"Clean"
    ==>"Deploy"

RunTargetOrDefault "Deploy"

I end up with a an error:

FsiEvaluationException:

Error:

        DeployScript.fsx(10,5): error FS0001: This expression was expected to have type
            unit
        but here has type
            int


Output: [Loading C:\Users\myusername\Desktop\SomeFolder\DeployScript.fsx]


Input: C:\Users\myusername\Desktop\SomeFolder\DeployScript.fsx
\Arguments:
  C:\fsi.exe

Exception: Yaaf.FSharp.Scripting.FsiEvaluationException: Error while compiling or executing fsharp snippet. ---> System.Exception: Operation failed. The error text has been print the error stream. To return the corresponding FSharpErrorInfo use the EvalInteractionNonThrowing, EvalScriptNonThrowing or EvalExpressionNonThrowing
   at Microsoft.FSharp.Compiler.Interactive.Shell.FsiEvaluationSession.commitResult[a,b](FSharpChoice`2 res)
   at Microsoft.FSharp.Compiler.Interactive.Shell.FsiEvaluationSession.EvalScript(String filePath)
   at Yaaf.FSharp.Scripting.Helper.evalScript@1303.Invoke(String arg00) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1303
   at Yaaf.FSharp.Scripting.Helper.save_@1276-2.Invoke(Unit unitVar0) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1277
   at Yaaf.FSharp.Scripting.Helper.consoleCapture[a](TextWriter out, TextWriter err, FSharpFunc`2 f) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1221
   at Yaaf.FSharp.Scripting.Helper.redirectOut@1247[a](Boolean preventStdOut, OutStreamHelper out, OutStreamHelper err, FSharpFunc`2 f) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1254
   at Yaaf.FSharp.Scripting.Helper.save_@1275-1.Invoke(String text) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1276
   --- End of inner exception stack trace ---
   at Yaaf.FSharp.Scripting.Helper.save_@1275-1.Invoke(String text) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1284
   at Yaaf.FSharp.Scripting.Helper.session@1306.Yaaf-FSharp-Scripting-IFsiSession-EvalScriptWithOutput(String ) in C:\code\fake\paket-files\matthid\Yaaf.FSharp.Scripting\src\source\Yaaf.FSharp.Scripting\YaafFSharpScripting.fs:line 1308
   at Fake.FSIHelper.runScriptUncached(Boolean useCache, String scriptPath, IEnumerable`1 fsiOptions, Boolean printDetails, CacheInfo cacheInfo, TextWriter out, TextWriter err) in C:\code\fake\src\app\FakeLib\FSIHelper.fs:line 471
DeployScript.fsx(10,5): error FS0001: This expression was expected to have type

The point here is I'm trying to do a shell command only under a certain target. Pay no attention to the mkdir command as I actually would like to use the schtasks command. I just used mkdir for simplicity purposes. Maybe there's a nuance that I'm missing here. I've also noticed this same behavior with using environVarOrFail. Thanks in advance to all who reply.