Index-cache.yaml for Chart repo was NOT been reflected into cache file index.yaml after restore on disk during backup/restore operation, so out-of-date display on portal

Expected behavior and actual behavior:
chart file can not be restored on harbor portal but available under chart repo directory on disk (cinder disk used)

Steps to reproduce the problem:

On harbor portal, load chartA, chartB and chartC into chart repo
perform backup operation, e.g. backup chart related .tgz files and index-cache.yaml (--disable-statefiles flag was false by default)
On harbor portal, select chartA and remove it, observed chartA related .tgz removed and timestamp of index-cache.yaml updated, also only chartB and chartC visible on harbor portal
perform restore operation, e.g. move the backup file in step#2 back into chartmuseum repo related directory, so three chart related .tgz and original index-cache.yaml were back again there.
but on harbor portal, still only 2 chart files visible, chartB and chartC, no help for refresh

Not sure why no try to reload the original index-cache.yaml to reflect the index.yaml, and any sync up issue between statefile index-cache.yaml and cache file index.yaml??

Versions:
Please specify the versions of following systems.

harbor version: [2.4.0]
docker engine version: [19.03.14]
chartmuseum version: 0.13.1 or later