Mac or windows? What version of FileMaker?
Sorry. Mac OS 10.12.2 and FM Pro 15.
Try removing all text formatting. Somehow, the Helvitica font designation appears to be pasted with your text into the field. Any such formatting supersedes any formatting specified for the field while in layout mode. Thus stripping out the text formatting leaves plain text to then be formatted by the styles specified for the field object.
A common method for stripping text formatting from pasted text is to add this expression as an auto-enter calculation:
TextFormatRemove (self )
Make sure to clear the "do not replace..." option and keep in mind this only affects future edits on the field, this change won't automatically update existing data.