Comment 14 for bug 1335323

I don't believe the current behavior is documented. As far as I can tell, ASDF always reserves the right to cache everything. Caching is essential for the performance of ASDF 3. Without the cache, performance would go from O(n) to at least O(n^2) and maybe much worse — and was indeed an order of magnitude slower on actual systems in some configurations. With the cache, ASDF 3 is of comparable speed with ASDF 2 despite doing much more, for the sake of correctness.

So far, there is caching for both find-system and locate-system — see how they use with-asdf-cache. Actually, the general purpose cache on find-system catches cases of infinite loops for which special structures were used in ASDF 2 (see with-system-definition in ASDF 2.016 and later), as notably reported by you in the context of using Quicklisp.