I have three test case fields, all are text, all have markdown enabled. They are effectively mirrors of each other with the exception of different Labels, Descriptions, and System Names.
See screenshots for details. Let me know what other information would be useful to debug this anomaly. Screenshots located at http://imgur.com/a/Fc2xp
Edit 0: Further investigating is showing that this field works in other cases. I thought that maybe the ()'s were causing an issue, but removing them did not change anything