I've started getting this warning from Hugo:

WARN  deprecated: the ":filename" permalink token was deprecated in Hugo 0.144.0 and will be removed in a future release. Use ":contentbasename" instead.

However, changing the permalink format to use :contentbasename instead of :filename breaks my URLs. For example, /2025/05/05/2025-05-05-BA-on-border-disputes.html becomes /2025/05/05/2025-05-05-ba-on-border-disputes.html (note that "BA" becomes lowercase) via the filename "2025-05-05-BA-on-border-disputes.md".

Removing the :filename option would break my URLs due to the loss of case sensitivity.

What version of Hugo are you using (hugo version)?

$ hugo version
hugo v0.147.2+extended linux/amd64 BuildDate=unknown

Does this issue reproduce with the latest release?

Yes