Team Foundation Server 2015 TestCategory not working - tfs

Question

TFS 2015 is calling tests that do not have the "Dev" test category.
TFS Build has a Visual Studio Build and Visual Studio Test step. The Test step has TestCategory=Dev set in the Test Filter criteria.
Test Class
[TestMethod]
[TestCategory("Dev")]
public void AllOrderItems() {
//Assertions here.....
}
Log Results
2016-05-17T18:11:07.5722452Z ##[debug]Entering script VSTest.ps1
2016-05-17T18:11:07.5732446Z ##[debug]vsTestVersion = 14.0
2016-05-17T18:11:07.5732446Z ##[debug]testAssembly = **\*tests*.dll;-:**\obj\**
2016-05-17T18:11:07.5742465Z ##[debug]testFiltercriteria = TestCategory=Dev
...
2016-05-17T18:11:08.1743177Z Executing C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\CommonExtensions\Microsoft\TestWindow\vstest.console.exe "C:\TestAgentWork\35\s\APP.Business.Tests\bin\APP.Business.Tests.dll" "C:\TestAgentWork\35\s\APP.Business.Tests\bin\Test\APP.Business.Tests.dll" "C:\TestAgentWork\35\s\APP.Models.Tests\bin\Debug\APP.Models.Tests.dll" "C:\TestAgentWork\35\s\APP.Models.Tests\bin\APP.Models.Tests.dll" "C:\TestAgentWork\35\s\APP.Models.Tests\bin\Test\APP.Models.Tests.dll" "C:\TestAgentWork\35\s\APP.Web.Tests\bin\APP.Web.Tests.dll" "C:\TestAgentWork\35\s\APP.Web.Tests\bin\Test\APP.Web.Tests.dll" /TestCaseFilter:"TestCategory=Dev" /logger:trx
...
2016-05-17T18:11:10.6976251Z ##[error]Error Message:
2016-05-17T18:11:10.6976251Z ##[error] Assert.IsTrue failed.
2016-05-17T18:11:10.6986243Z ##[error]Stack Trace:
2016-05-17T18:11:10.6996235Z ##[error] at APP.Business.Tests.BusinessLayerTests.CheckIfCertifierSignatureOnFile() in C:\TestAgentWork\35\s\APP.Business.Tests\BusinessLayerTests.cs:line 516
2016-05-17T18:11:10.6996235Z Failed CheckIfCertifierSignatureOnFile
I've also tried priority=1 and added [Priority(1)] as an attribute on the test method with the same results.
TFS Version 14.95.25122.0

Answer 1

Just tested with TFS 2015 Update2, Test Filter Criteria worked as expected. Please make sure your TFS has upgraded to the latest edition.
Also, the error message "Assert.IsTrue failed" indicates the issue is due to your test methods, you may check them.