I've created a new drawing using ANSI standard inch dimensions. When I open Tools>Documents>Units and change to Custom, Feet & Inches, new dimensions I create in the drawing are inconsistently applied. Some show up in Feet & Inches, others in decimal inches. They seem to be worse if I dimension to centerlines that were created before I switched, but even that's not 100% of the time.
I can duplicate the glitch. Just create a new part with two elements you can apply centerlines to, make an ANSI format drawing from the default templates, generate some centerlines, then switch units to Feet & Inches, then try to dimension the part. Dimensions to the centerlines frequently fail to use the new units for me.