That is bizarre, I opened your file and the same thing happens, bringing the data in as a layer or a shapefile. What is even stranger is when you do a select by attribute on the field and hit get unique values, it just shows the "Certain" "Probable" and "Uncertain", not those with the delimited values. Even re-doing the values in ArcMap does not fix the issue, I selected each attribute and did a field calculator on each with the string certain, probable, and uncertain and it still shows "Certain , 1, 1" etc. in the unique values symbology.
So now you know its not just you. As for a solution, I'm a bit stumped so far.