Importing P12 into Keychain access fails due to incorrect password

When importing a P12/PFX file into Keychain Access in macOS 13.5 it fails with an incorrect password message. The same P12/PFX file imports successfully into Firefox. Both the private key and certificate can be extracted using openssl.

The P12 contains a private key and certificate signed using my own root CA (self signed). The P12 file is used for mutual SSL for a website which requires mutual SSL.

It looks like a recent update has broken the P12/PFX import functionality. P12s/PFXs which have already been imported are still present and work as expected.

Is anyone else having a problem? What has Apple changed? It looks like a software bug around the password handling of a P12 in macOS Keychain Access.