It seems you find a bug, but I can not reproduce it.
- Could you tell me which version of LDT you use? (nightly build ? 0.9.0M1 ?)
- where do you set this argument ? (in the launch configuration dialog, in the interpreter preference page)
I just try with your argument, and it looks like a bug.
Could you, please, file a bug about it?
We will fix this. In the meanwhile, you might be interested in a workaround.
You may try to define your arguments without spaces or double quotes.