HP 15c Collector's Edition save/restore does not work

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I just received my HP15C "enhanced" from TheCalculatorStore and letting aside that I got the wrong overlay (aviation), I have one major issue. While the firmware looks OK (Checksum 0A0A) and I could read out the firmware image with Sam-Ba and check that it's identical with the one from hpcalc.org (HP_IAR_USB 120ms.bin), I did not succeed in connecting the calcultor in HID mode to neither of my PCs.

On my desktop PC (Win10) just nothing happens at all. If I switch on the HP15C with "Enter+f" pressed, there is no device recognized at all (no connection sound, no new device listed anywhere).

When I try the same on my Notebook (Win8), there is an "HID-compliant vendor-defined device" (or something like that) found which also disappears when I remove the USB connection, but it's not displayed as HP10bII+ and not recognized by VoyagerSave, either. Actually, in the device manager the device is shown as "not working", which is probably the reason why it's not working as expected.

Even worse, usually the HP15C freezes and the only way to even switch it off again is to reset it (through the cable or the reset button). Contradicting the description where pressing On would switch the calculator off and leave USB mode, it doesn't react to any key at all.

In a nutshell, letting aside that neither of my two Window PCs recognizes the HP15C CE (correctly) in USB mode, the calculator seems to freeze when trying to enter USB mode and needs a hard reset.