You know what else? I bet if you look in your registry in Windows that you'll see registry keys from software that you've uninstalled before!
Shocking!
They're called "remnants". You do NOT have a hybrid firmware. It's just leftover files.
Since nothing in the 1.5 "update" ever wrote to that directory, then it's not going to "remove" it or write over it. The flash in the PSP isn't like that of a router or something, where you flash a new firmware and it completely obliterates everything else in the flash by writing over it.
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