I don't know if this is by design or not because I've only recently been trying to force myself to use Intellirush so that I can compare against R#. I have noticed that Intellirush will cause an extra period to be put on my attached properties when I'm typing the attached property into an element.
When I type:
<Label Grid .
Intellirush adds a period for me even though I have completely typed the word Grid. So I end up with:
<Label Grid ..
I don't think that Intellirush should be adding an extra period.
I've also noticed that if I use the . to complete after typing just Gr then it will add an extra period as well. This is not how the Intellirush auto-completion stuff works for me anywhere else, including in non-Attached Property contexts.
Attached properties are the only place I've noticed Intellirush acting funny in Xaml. Intellirush seems to be okay with Element level completions. (Label.Style, etc)