I just run the demo application of the TaskDialog and the button placement is not as it should be (this is ugly looking) because there is no space between the button and the border. I have included a picture. When watching the YouTube demos of TMSFNCTaskDialog the button placement is as it should be because it has some pixels between the button and the border.
I just ran 11.1 for the first time and find the same issue. Using VCL. In FMX it seems to work correctly.
I also note that there is no padding on the right side of the dialog. You can't really tell on this one because of the way the words wrap. But on others, the in the instruction property runs all the way to the right edge.
I will send you screen shots.