Caching warnings are completely wrong

I’ve been running some tests and keep getting a low score for “cache static content”. When I look at the details it shows several images as only being cached for a few days (3.1 days, 2.6 days, etc).

Here’s one example:

But those images are all cached for a long time. Checking the Response headers on the waterfall chart shows my correct setting of 30 days:

I also double checked on other tools and the caching is fine. Is there something wrong with WPT? Or is there some other reason it thinks the caching is so short?

I think it’s subtracting the value of the Age header from Cache-control’s max-age. I don’t think that’s correct - afaik, Age just tells you how long the proxy (Cloudflare in this case) has had it cached already - nothing to do with the how long the browser will cache it. But I could be wrong.