Debug help - Programming in D - extending tail slice terminates sharing unexpectedly. Page 69, 70

[Brother Bill]

The program starts with a dynamic slice of odd integers 1 thru 15.
Append 17 and reassign to slice.
Declare dynamic slice tailSlice of the second half of slice.
Check the length of tailSlice, which is 5; and capacity of 
tailSlice, which is 7.

Since capacity > length, we ought to be able to add two integers 
to tailSlice without terminating sharing of slices with slice.
But incrementing the length of tailSlice by 1 breaks sharing.
This is unexpected.

Am I missing something, or have I (unlikely) found a bug in the D 
compiler?
What is the explanation of this behavior?
I would expect that increasing the length of tailSlice ought to 
continue to have sharing with slice.

source/app.d
```
import std.stdio;

void main()
{
	int[] slice = [1, 3, 5, 7, 9, 11, 13, 15];

	slice = slice ~ 17;
	writeln("slice: ", slice, " length: ", slice.length, " capacity: 
", slice.capacity);
	writeln();

	int[] tailSlice = slice[$ / 2 .. $];
	writeln("slice: ", slice, " length: ", slice.length, " capacity: 
", slice.capacity);
	writeln("tailSlice: ", tailSlice, " length: ", tailSlice.length, 
" capacity: ", tailSlice.capacity, " &tailSlice[0]: ", 
&tailSlice[0]);
	tailSlice.length += 1; // fails here
	// tailSlice ~= 0; // also fails
	writeln("tailSlice after incrementing length by 1: ", tailSlice, 
" length: ", tailSlice.length, " capacity: ", tailSlice.capacity, 
" &tailSlice[0]: ", &tailSlice[0]);
	tailSlice[0] = 888;
	writeln("After tail slice length increase and changing 
tailSlice[0] to 888. ", " length: ", tailSlice.length, " 
capacity: ", tailSlice.capacity);
	writeln("tailSlice: ", tailSlice);
	writeln("slice    : ", slice);
}

```

Console output:
```
slice: [1, 3, 5, 7, 9, 11, 13, 15, 17] length: 9 capacity: 11

slice: [1, 3, 5, 7, 9, 11, 13, 15, 17] length: 9 capacity: 11
tailSlice: [9, 11, 13, 15, 17] length: 5 capacity: 7 
&tailSlice[0]: 26AAAA31040
tailSlice after incrementing length by 1: [9, 11, 13, 15, 17, 0] 
length: 6 capacity: 11 &tailSlice[0]: 26AAAA31060
After tail slice length increase and changing tailSlice[0] to 
888.  length: 6 capacity: 11
tailSlice: [888, 11, 13, 15, 17, 0]
slice    : [1, 3, 5, 7, 9, 11, 13, 15, 17]

```