The grade is being calculated because values entered in a scale are seen as strings of text and then calculated based on the total number of possible values. As an example, a scale of "F, D, C, B, A" is the same as "Cat, dog, fish, bird, elephant". The value choices are simply selections you can choose from; that are then displayed to students.
The grades/percentage that is then displayed to students based on what value choice was selected, is dependent on your aggregation type. So in your example scale, there are 126 different choices to select from. If a student was given "F/A-", that is the 11th choice from the bottom of the list. This means Moodle is going to convert it to 11/126 or 10/125 depending on your aggregation type.
As a personal recommendation, I have my faculty users avoid scales because most do not understand what a string of text means. Some have created scales like "0, 1, 2, 3" or "3, 2, 1, 0". Both are the same in that they have four values. One is backwards but that doesn't matter as they are seen as strings of text. Furthermore, depending on their aggregation type, Moodle will convert these to be either 1-4 points possible or 0-3 points possible.
I recommend checking out the Moodle Docs on scales as it has some better examples than mine. If you want to allow your instructors to continue to make scales like this but don't want Moodle to convert it to a percentage and thus towards the course total, go into Site admin > Grades > General Settings > Include scales in aggregation and uncheck the box.
Happy 
oodling!
