Usually when I copy-and-paste-special-value a numeric value,
the target cell gets exactly the same binary value that the
original cell had.

But I stumbled upon one case (I'm sure there are others) where
that is not true. That is, the pasted value has a different binary
representation.

Under what conditions does this happen?

Consider the following two examples. (The binary value is on
the right. I use Excel 2003.)

1. Unusual(?) case.

A1: 2.00666666666667
A2: =100*round(A1,2) // &h40691FFF,FFFFFFFF
A3: 201 // &h40692000,00000000
A4: copy-and-PSV from A2 // &h40692000,00000000

A2 displays the same character repesentation as A3, even in
Scientific format with 14 DP. But the binary values differ
by 2^-45. As shown, the pasted binary value of A4 is the
same as A3, not A2.

2. Usual(?) case.

B1: 0.999999999999972 // &h3FEFFFFF,FFFFFF04
B2: =B1 - 2^-53 // &h3FEFFFFF,FFFFFF03
B3: copy-and-PSV from B2 // &h3FEFFFFF,FFFFFF03

Again, B1 and B2 display the same character representation
in Scientific with 14 DP. But the binary values differ by
2^-53. Contrary to Example 1, the binary value of B3 is the
same as B2, not B1.

I say "contrary" because to explain Example 1, I hypothesized
that when a value is copied to the Clipboard, Excel converts
the binary value to its most precise character representation,
then converts from the character representation to binary when
we PSV. Example 2 seems to contradict that theory.

Every other theory I've hypothesized does not seem to explain
when PSV will and will not change the binary value.

Example 2 differs by a much smaller amount than Example 1.
The difference in Example 2 is even a slightly smaller percentage
(about 1.11E-16) of the binary value associated with the character
representation than the difference in Example 1 (about 1.414E-E16).

Both examples differ in the least-significant bit. And the LSB
differs in the same "direction", namely from odd to even, which
may be significant when considering the (default) rules for
rounding
from 80-bit to 64-bit floating-point in the Intel FPU.