Spelling an unwritten langauge
Grace Wiebe has for over 10 years worked on creative spelling of adult speakers of an unwritten dialet of Low German. Here is the most recent paper on the topic:
Wiebe, G. Adults’ creative spelling of an unwritten language: Literacy and awareness of phonological units. Derwing Festschrift. (accepted). View Article
These adults are literate in English and/or German, but when asked to spell their dialect, which has no orthography, they had to think hard how to analyze and represent the phonology, particularly consonant culsters. For example:

Being native speakers of the dialect, there is not doubt that their underlying representation (or Input) of the word is NOT how they spelt them. In other words, Faithfulness between the Input (phonology) and the Output (orthography) is violated. But by whom?
One explanation is that they were using a foreign orthography, one that does not fit their native phonology. Some of the sounds or clusters may be hard to find correspondences in the English or German alphabet. The spellers had to scramble to find the "closest" approximation.
On the other hand, isn’t it true that even the "native" writing system is not perfect for representing phonology?