Testcase working but not in LoadTest

Hi,

I just made a TestCase with SoapUI 4.0.1 which works quite fine.
A unique ID is generated with Groovy and saved in Properties

testRunner.testCase.testSuite.getTestCaseByName("LoadTest-Initial").setPropertyValue("bUID","$UID")

The ID is used by a rest TestRequest-Body (REST)

{"uid" : "${#TestCase#bUID}"}

All that works fine when I start the test.
But when I add TestSteps to LoadTest the id is not read from TestCase-Properties. If i let it run multiple times I can see, that the bUID is updated in Properties, but not used in Request.

Do you have any advise how I can find the error...
Are there any differences running a test as Load-Test?

Thank you
Haiperlink