One possibility: I'm running Energizer "e2" batteries rather than NiCds -- sometime today I'll fetch my 34c and swap in the rechargeables and see if the voltage difference changes anything.
Meanwhile, however I'm messing with a 31e at an advertised 3 volts, and . . .
I see two distinct forms of "ghosting". The minus sign flashes, and commas appear, whenever there is a "2" in any position in the display.
It appears that the brightness of the minus sign's flash is directly related to how many 2's are being displayed. That's weird, and it doesn't seem to appear with any other digits, in any combination. But whenever 2's are in the displayed value, the minus sign flashes, and the more 2's in the display, the brighter the flash.
The ghosting appears identically with whatever keypress results in a particular display.
The flashing commas are really weird.
I'm experimenting after setting <f> <FIX> <9>, entering something like "0.020020002" and pressing <+> or <ENTER> repeatedly. With this example, the ghosting display shows briefly "-0.020,0200,02" . Notice the positions of the decimal point and ghosting commas relative to the 2's.
A few more examples with 2's and 0's:
0.2 0 0 2 0 0 0 2 0
-0.2 0 0,2 0 0 0,2 0
0.0 0 2 0 0 0 2 0 0
-0.0 0 2 0,0 0 2 0 0
0.0 0 0 2 0 0 0 0 2
-0.0 0 0 2 0,0 0 0 2
So it seems the ghosting commas appear, relative to the 2nd & subsequent 2's, in postitions analogous to that of the decimal point relative to the first 2.
Erk.
Then it gets weirder yet.
A few more examples, this time with 2's and other mixed, zero and non-zero digits:
0.3 0 2 0 0 2 0 0 0
-0.3 0,2 0 0,2 0 0 0
0.0 1 1 1 2 3 4 5 2
-0.0 1 1,1 2 3 4,5 2
1.0 2 3 4 2 5 6 7 2
-1.0 2,3 4 2,5 6 7 2,
So it seems the ghosting commas actually appear, relative to 2's following any non-zero digit, in postitions analogous to that of the decimal point relative to the first non-zero digit.
Double-erk.
I'm sure there's a (perhaps not-so-straightforward) physical explanation for this behavior, but it is a different case!
But now, I've been staring at my calculator display a bit too long -- time to get back to life . . .