Such a workaround with 2 rules could be something like

.SECONDEXPANSION:
all: lib/hello.o hello.o
%.o: 3$$*.c; $(info $@ from $<)
lib/%.o: lib/3$$*.c; $(info $@ from $<)

What I usually do is recommend people use $$* instead of % in secondary expansion expressions like this as it's more clear and less confusing, and ends up being the same result.

I'll look at this change.

Make fails to substitute % with the stem in prerequisites of pattern rules when second expansion is enabled.

E.g. given makefile

.SECONDEXPANSION:
all: hello.x
%.x: $$(wordlist 1, 99, %.1 %.2) $$(wordlist 1, 99, %.3 %.4); $(info $@ from $^)

make fails to substitute '%' with 'hello' in '%.2' and '%.4'.

Specifically, make substitutes the first % in each 'word', where 'word' is determined by get_next_word. In the example above, '$(wordlist 1, 99, %.1 %.2)' and '$(wordlist 1, 99, %.3 %.4)' are such 'words'.