We tested the ramp with a simple example and did not have the same problem.
You can have two ramp variables with the same name, so one suggestion is to double check you have the proper one selected. Other than that it is hard to say without seeing the file, because what you sent looks like it should work.
You could also try to simplify the command as much as possible, no masks, no labels, etc. and see if you have the same problem.
You are also welcome to use the email link under the help menu in DataGraph, to send us your file, or one with the same problem but made up data.