HP35s: unexpected behaviour with LASTx

[Dieter]

Some time ago I found a somewhat strange behaviour of my 35s with LastX and Pi.
Maybe you can try this:

Code:

2 [ENTER] 5 [x]           10,0000
3 [LASTx] [x]             15,0000

So far, so good. After the first multiplication LASTx was set to the last factor 5, so the second calculation returned 3x5 = 15.

Now do the same with Pi instead of 3.

Code:

2 [ENTER] 5 [x]           10,0000
[π] [LASTx] [x]           31,4159

After pressing [LASTx] not the expected 5 appears, but the last result 10. It actually looks like pressing the [π] key causes the current X to become the new LASTx. So the result is not the expected 5π but 10π.

You may even try this:

Code:

[CLSTK] [x]              0,0000   clears the complete stack including LastX
123 [π]                  3,1416   enters 123 and Pi
[LASTx]                123,0000   obviously 123 has been moved to LastX

BTW this does not seem to happen with other constants, e.g. in the first example, [e] [LASTx] [x] returns e*5 = 13,5914.

Any ideas what's going on here?
May this be a firmware bug that sets LASTx when π is entered?
The 35s seems to behave as if π was a function π(x).

Dieter