Nobody explicitly decided to enable the logging by default. It was caused by an uninitialized variable. Uninitialized variables result in undefined behavior, but can often go unnoticed in practice if the code around them results in the value in memory (or register) for that variable usually being a certain value. In this case, it happened to result in logging being disabled by default in most situations. But using jemalloc for the process rather than the standard malloc implementation was enough to cause the opposite result, apparently due to jemalloc poisoning malloc()ed regions (which overwrote the "usual" value).