Changes to stan models in source not recognized -- "make: Nothing to be done for 'all'."

When building ctsem (using rstantools), I'm encountering this all of a sudden -- after some small changes to the stan files, I run rstan_config() and double check that the source files are changed, but when I build, compilation is for some reason not triggered. If instead I delete the relevant source files and build, compilation works normally and everything is as expected. Any ideas welcome... 