I have attached an example solution for you to see what I mean. When you run my program you will see the image of the slide on the form and you would see a small square appearing in front of the text box with the text "Account Name". The text box is not created using the Powerpoint program but problematically creating using the PPOM using vb.net. This happens to any object that we create.
Sorry, we were busy with other tasks and just have started to work with your problem. Please check attached screenshot of the image created with you app. There are no any squares.
It looks like you are testing on a Windows Vista machine (I figured it out from your screen shot). My screen shot was from a Windows XP machine. Hence I tested on a Vista machine here and it confirmed that this problem occurs only on XP. Since our generation runs on client machine and since we cannot control what operating system our clients use, it would be great if you could resolve this issue.
As I wrote, that is not a problem of Aspose.Slides. You should create correct presentations. Disable bullets or use some real characters for example space if you don’t want to see it.