The behavior of tab canvases ist very interesting, when your form gets more and more tabpages.
Let's say, you have only three pages in your tab canvas. (Width Style Property = Fixed)
In the next step we create a fourth tab:
If there is not enough space for all page-labels in the same size, then we see a first kind of resizing. All labels are readable. But the size of some pages is reduced.
If we create more tabpages:
And in the last stage:
The last type of look and feel is, when we get a horizontal scrollbar. Think on this, when you use many tabpages in your form