Issue: When using PageSpeed debugging query string, filters that was previously not active under PageSpeed settings are being turned on.
e.g. If you only had image_rewrite filter enabled in PageSpeed, when you navigated to www.example.com/?PageSpeedFilters=+debug the resulting page contained other filters that were not enabled, such as rewrite_css, rewrite_javascript etc.
This is because the =+debug directive is working off the corefilters rewriting level seen here: https://modpagespeed.com/doc/config_filters.html#level
Solution: The way to test with only your enabled PageSpeed filters is to explicitly list the filters in the URL using = instead of =+ with comma separators.