Thanks defragster. To be clear, Teensyduino and its teensy uploader works perfectly. Its a problem with PlatformIO in Windows. Its interested to see Stino being developed again, I abandoned it a year or so when it became unsupported.
However, I use PlatformIO for more than my desktop dev environment. It powers a deploy process where I develop on my windows desktop and then deploy to GIT. An embedded Ubuntu system (Console only - Intel Turbot) tracks a git repository, updateing a Spring/Java application server and rebuild+deploys changes in companion C++ code directly to a connected teensy micro-controller.
Open to any better ideas, though I have to say it all works pretty well outside of my windows issue.