Hi,
I noticed that CLSTK not only clear the stack, but also registers L and I, so LastX value is lost after performing a CLSTK. I have revision 1728 in my 34s and I am using revision 1747 on my computer. In both of them I see the same result.
Of course, other calculators as the 42s or the 35s, preserve LastX after clearing the stack.
Regards,
Miguel