Running Testcase multiple times takes longer to finish

I have created a TestCase in SoapUI for my project. It contains only one teststep.
When running this in the UI (on windows) everything goes fine.
Running this from the commandline (on windows)  everything goes fine as well.
But running this from the commandline on a Linux machine shows some strange behavior.

The first run: [SoapUITestCaseRunner] soapUI suite [TestSuite] finished in 1273ms The Second run:  [SoapUITestCaseRunner] soapUI suite [TestSuite] finished in 107620ms
Thrid run: [SoapUITestCaseRunner] soapUI suite [] finished in 112608ms

While the testcase itselfs always takes less than a second:
[SoapUITestCaseRunner] Finished running soapUI testcase [TestCase], time taken: 255ms, status: FINISHED

When I wait 2 minutes, and then run the test again, it is back to a less than 2 seconds.

The webservice itself runs on the Linux machine, so from windows I connect to a remote ws, while the testing on Linux connects to localhost.

Anybody any idea why testing on Linux shows this strange behavior.

Environment:
SoapUI: 2.5.1
Windows: xp - sp1
Linux: SUSE LINUX Enterprise Server 9 (i586), VERSION = 9, PATCHLEVEL = 2