Oracle 12.1.0.2 on Windows7, Oracle commands hung in mswsock.dll

[MartinG3]

I am trying to install Oracle 12.1.0.2 on Windows 7 running under Parallels on my MacBook Pro (Retina, 15-inch, Mid 2015).
However, some of the Oracle command-line tools are hanging just before they should terminate. Example commands are "lsnrctl" and "tnsping". Taking the latter as an example:

C:\Users\mgd>tnsping 10.4.8.150_UNICODE

TNS Ping Utility for 64-bit Windows: Version 12.1.0.2.0 - Production on 06 OCT-2015 14:10:48

Copyright (c) 1997, 2014, Oracle. All rights reserved.

Used parameter files:
C:\oracle\product\12.1.0\dbhome\network\admin\sqlnet.ora


Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)
(HOST = 10.4.8.150)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = unicode)))
OK (20 msec)
...program hung here for minutes...​

In this case the command did what it should (see the last line "OK (20 msec)") and was expected to terminate immediately after.
Using Sysinternals (Microsoft Technet) Process Explorer, I got a stack trace from the hanging process:

ntoskrnl.exe!memset+0x61a
ntoskrnl.exe!KeWaitForMultipleObjects+0xd52
ntoskrnl.exe!KeWaitForMutexObject+0x19f
ntoskrnl.exe!PoStartNextPowerIrp+0xba4
ntoskrnl.exe!PoStartNextPowerIrp+0x1821
ntoskrnl.exe!KeWaitForMultipleObjects+0xf5d
ntoskrnl.exe!KeRemoveQueueEx+0x323
ntoskrnl.exe!ExQueryAttributeInformation+0x1803
ntoskrnl.exe!MmLockPagableSectionByHandle+0x655
ntoskrnl.exe!KeSynchronizeExecution+0x3a23
ntdll.dll!NtRemoveIoCompletion+0xa
mswsock.dll+0x5941
kernel32.dll!BaseThreadInitThunk+0xd
ntdll.dll!RtlUserThreadStart+0x21​

To me it looks like the process is stuck waiting for a Windows Mutex as part of some network operation in the Winsock layer (mswsock.dll) - maybe as part of network shutdown for the process.

Does anybody have an idea of what is wrong or have you seen similar behaviour with other "client" software?