So by home screen you mean the screen that was being displayed when the phone was locked. Right?
I must have read what you wrote in your first msg incorrectly. I understood you to say/mean, that you went from a "slide to unlock" screen directly to the home screen when you depressed the home button, without the phone unlocking. I took that, I believe, directly as you wrote it.
Again, if you were using a registered finger to depress the home button to cause that to happen, THAT is what unlocked the phone.
Question: Try it again, but don't use a registered finger. Did the phone gp to the home screen?
Sorry if I'm not understanding it. If your phone is not unlocked, you're either going to get a "try again" prompt or a "slide to unlock" prompt. From there you said:
"On a whim, I depressed the home button, and I was taken instantly to the home screen, without any unlock being required."
So what I read in what you said was, from a locked phone condition, or in your words, "slide to unlock", you unlocked your phone by "depressing the home button" with, and I'm assuming this, as you did not state if you depressed it with a registered finger or not, with a registered finger, you unlocked the phone.
I don't see any issue other than, it worked as expected.
Now if you went from the "slide to unlock" prompt and hit the home button with a non-registered finger and it then went to the home screen, then something is very broken.