HP41 backarrow to CLX behavior

[hth]

I discovered a strange behavior in the HP41 digit entry and wonder if this is a bug.

When I enter a number and then backarrow up to rub out every digit, I end up with 0 in the display and stack lift disabled. It did a CLX.

However, if I press and hold the backarrow key at the last digit, I get CLX shown followed by NULL. Now release the key and I also have 0 in the display, but with stack lift ENABLED.

First of all, I cancelled the operation, should it not go back to showing the last digit again?
Second, why is stack lift enabled? Well, I guess it cancelled the CLX, but still it stored a 0.

You can try as follows:

Get 7 and 5 on stack with stack lift enabled:
2 ENTER 5 + LASTX

Start digit entry :
3_

Press and hold <- (until NULL)
Gives 0

Now try to add 1:
1 +

HP41C now shows 1, RDN gives 5.

If I do not hold backarrow (or try this on an HP16C), I get 6, RDN gives 7.