unit tests fail on windows (/C:/cygwin/... is invalid)

Under windows, I get the following exception from some of the unit tests:

java.io.IOException: Invalid file name: /C:/cygwin/home/hadoopwin/owen/hadoop/build/test/mapre
d/local/50062_0/taskTracker/jobcache/job_0001/task_0001_m_000002_0/.split.dta.crc
at org.apache.hadoop.dfs.FSNamesystem.startFile(FSNamesystem.java:416)
at org.apache.hadoop.dfs.NameNode.create(NameNode.java:238)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:337)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:538)