I had something similar to this happen with a dropdown. What I did to keep the drop down from grabbing focus ever time the user would hit the space bar was to put the drop down in its own page and on the page I added the following code.
Code:
OnHoverIn="dorpdown.Enabled=True"
OnHoverOut="dropdown.Enabled=False"
You can not add this code to the Object in question because once you !Enable it it will no longer fire it's events.
It may or may not work with a text box, I've never tried with a textbox object.