For example: I have a lady known as Mary Ann, surname N/A. Up to now, I have left surnames blank for such folk and not had a problem. Eventually, I find the surname for most of them. However, when I exported the FH6 GED file to Heredis on my iPad ready for a session at the local Record Office next week, she has transmogrified in Heredis into Mary ANN (Given Mary, Surname ANN).
Heredis appends UNKNOWN as the surname for any who are missing one, whereas FH shows them at the top of the Individuals list.
The FH6 entry for her is interesting, since it seems to support both interpretations:

The GED matches that (GIVN Mary, SURN Ann, but NAME Mary Ann //).
I have several more like that, and a goodly crop of Elizabeths who show as Elizabeth // but then are SURN Elizabeth in the GED file. Ditto Mary, Anne, and many other popular girls' names.
I can fix the problem (if problem it is) with Notepad and the GED file, but I wonder if there's a quicker, easier way.