ASDF recompile all files if ASD file is changed?!

Hi ASDF list, I have some huge generated Lisp files which took a lot of time to compile into fasl files. I put the sources into my ASD system definitions with other hand-written Lisp files in parallel (thus no dependencies at all). I found that, whenever I changed the ASD definition, if I load the system by ASDF:LOAD-SYSTEM, all Lisp files will be recompiled, even their source files are not changed at all. Is this a desired feature or possible issue? Do I need to provide sample code to show this “issue”? I’m using quite a recent ASDF (version: 3.3.1.7) Regards, Chun Tian