Follow-up to #5303. When deduplication shortens a thread ([[a, b], [b, c]] -> [[a, b], [c]]) and no frame changed, the fast path dropped [c] without clearing its threaded continuation. A thread that lost a listing now counts as changed and is flowed again.
Reflow copied each listed frame's text into its thread's story, so a
document that listed one frame several times in a thread, or in several
threads, repeated that text in the story and wrote the grown story back
for the next thread to copy again, growing the text with every
repetition while the document opened. Reflow now keeps each frame at its
first place in the thread list only.
Dylan M. Taylor