Bad Windows font, probably. It's just using the default system fonts, which in case of Segoe UI doesn't employ caps for I. Ironically, Segoe (just Segoe, the reference font) do have caps on I.

I stand corrected (I didn't look up the CSS, can't do that in Safari on iPad). That leaves room for improvement in my browser's default font then.

Note that system fonts usually can't be overridden in browsers, you need to inject custom CSS with the override.