Issue 111934

Steps to reproduce:
1) File > New > Text Document
2) Insert some text: for example, dt, F3
3) Edit > Selection Mode > Block Area: ON
4) Select a block through the middle of the paragraph, for example, a block that
matches the boundaries of the sentence "That didn't bode well." in the first
line of the dummy text, extended through all the lines of the paragraph.
5) Watch carefully the extent of the selection's right boundaries
6) Copy the selection to the clipboard (Ctrl+C)

Expected result:
Copy to clipboard should not change the selection

Actual result:
Copying to the clipboard causes the selection to be extended one character
toward the right on several lines.

See the attached screenshot for an example.

This does not always happen, but for a particular selection, it is mostly
reproducible. The exact result does seem to depend on exactly what is selected
and how the selection was made.

The changes always seem to be on the right side of the selection; I have not
seen the left-side boundaries change...

... Oops, I spoke too soon: if I start the selection at the right and move the
mouse up and to the left, then the boundaries on the left side change with copy.
It looks like the copy is somehow making a small change in the editing cursor
position and that triggers a change in the block selection boundary.

The problem is not that block selection is complex when the characters don't
fall in even columns, the problem is that the selection boundaries are changing
outside the user's control.