I tried to replicate the issue last night with using Sony Vegas Movie Studio Platinum 9.0, version 9.0 (b) build 92.
I engaged various text options under the Sony Media Generator: Simple Text, Rolling Text, and some legacy defaults. The only time I saw a Bounding Box was within the text pop up window where one has the option of placing text by dragging the box to where you want it to appear in the video. In no cases did I see the Bounding Box appear in the preview window nor were there any artifacts such as the persistent "42" that you demonstrated.
Due to the timing of the upgrade from v 8 to v 11 that you mention in the comments, I am thinking something went awry. The best thing I can recommend is to use the question form available at:
You will need to register with the site to access this service, and once you engage the form it will look something like this. You will need to give them the needed technical info like the version number and your machine info too. Here is a snip of the form to assist in that preparation. I have used this service many times in the past, and they generally offer very kind attention. However, you may have to wait a few days before they process your question depending on their current load.