Hi @cl1008,
Going on your description, it's likely that your grade did not change and that is actually correct. When assignment groups are weighed (the 25%), the total points earned for the assignments inside each group are divided by the total points possible for each group, then multiplies by the weight for each group and added together. What's likely happening for you is that you had 11/12 points in the group originally, then got another 11/12 points in the same group. Effectively your grade for that group stayed exactly the same (even though there are more points earned and possible), so your overall grade also stayed the same. Now if you were to get something different than 11/12 for the next assignment in that group, your grade would go up or down accordingly, but if you again score 11/12 your overall grade would remain the same.
Hope this makes a little sense at least and helps you out!
-Chris