Covariate Significance Testing - multiple covariate testing problem(s)

Hello, my name is Ikhsan and I have some questions regarding multiple covariate testing on the Covariate Significance Testing module.

Before that, I have followed the tutorial using the example dataset (bump**.vtk) provided and I got a positive result. I have also read some topics and discussions in this forum related to my following questions.

In my case, I would like to run a statistical shape analysis (group differences) on dentate nucleus and include age as a covariate. I have successfully performed and got the p-value from the group difference test between the controls and patients without any covariate. However, when I included another column (age) on my CSV file, it only showed the p-value for age and displayed no p-value difference in the controls vs patients.

I have tested my CSV file in the Shape Population Viewer and it functions properly. The picture below shows my screen capture of my shape analysis attempt; the p-value of controls vs patients, the p-value of age differences alone, and the p-value of both groups and age (the two images are the same file that I load twice to show the problem).

Could someone please give me suggestions on where I went wrong? Thank you in advance.