I have used both Winstep Extreme and IP together for several years now. I haven't seen that issue in Workshelf or Nexus, but it did crop up in Windows Explorer, the start menu and ObjectDock. There is a fix for that.
If the items you are adding are .exe's, try this:
Go to 'Start' open run command, type in Regedit.
In the new window of Registry Editor go to HKEY_CLASSES_ROOT\exefile\shellex and delete the subkey/folder 'IconHandler'
You may need to restart explorer and/or Winstep afterwards.