The first character is often auto-capitalized in many input fields by your mobile browser.

If a field is properly declared to be a password field (<input type="password" name="pwd">) of course ideally this wouldn't happen (plus, the characters get masked with stars, and hopefully what you type doesn't end up in your autocorrect dictionary, etc etc) - but it's full of shitty browsers out there.

GP was specifically referring to caps lock inverse, not initial character capitalization (which I agree is more likely to be the problem).

More like if your password has a caps in it and you forget it on mobile.