In your part file right mouse click on the dimension and take a look at the choices. Right under the bold header that says Dimension. . . (and lists the particular dimension you are highlighting) there will be the option to Link Values if it is not already linked or to Unlink Value. If it is linked the link name will appear in the dimension description in the parentheses so you'll know what it is linked to. By your description you have something inadvertently linked and may want to Unlink it.
a sketch chamfer links the two values by default, ie .10(link) x .10(link). when you change one, the other will change with it. A chamfer feature creates two independent dimensions, ie .10 x .10 which are not linked.