Thank you for your post.
If it works properly on one machine but not another, what is the difference between the machines besides the operating system?
Is this a repeating field? A portal?
Does this dashed line issue occur if you create a new layout with the same field and formatting?
Does the Inspector show anything out of the ordinary when compared to other fields?
Any other information you can provide may be helpful in narrowing down the possible causes.
We had exactly the same issue when converting an FM11 solution to 13.