When you have a tree view with extended selections of the
form:

Column 1 | Column 2 | ... | Column k | ... | Column n

(doesn't matter if expandable items or not). You will find that if you hide a column 'k' and drag from the blank viewport to select items moving up with the mouse, you will get the items twice. This is because QTreeViewPrivate::columnRanges returns more ranges than expected when there are hidden columns in the middle of ranges. For instance, this is what I get for a test case:

Without the patch:

selection is
(QItemSelectionRange(QModelIndex(9,0,0x8109740,MySortFilterProxyModel(0x80888c0) ) , QModelIndex(9,2,0x8109740,MySortFilterProxyModel(0x80888c0) ) )
,

QItemSelectionRange(QModelIndex(9,0,0x8109740,MySortFilterProxyModel(0x80888c0) ) , QModelIndex(9,2,0x8109740,MySortFilterProxyModel(0x80888c0) ) )
)

With the patch:

selection is
(QItemSelectionRange(QModelIndex(9,0,0x80f13c8,MySortFilterProxyModel(0x80c5968) ) , QModelIndex(9,2,0x80f13c8,MySortFilterProxyModel(0x80c5968) ) )
)

As you can see without the patch when asking for selection() on the
selection model you get twice the same range (what makes for example
drag & drop to have the same information twice).

It is important to note that this happens when you drag from bottom
(blank viewport) selecting items going up, but as shown here:

Column 0 | Column 2 (Column 1 hidden)
items
items
items
x < click here (and move vertically up)

if you click like this:

Column 0 | Column 2
items
items
items
x < do not click here

the algorithm will correctly create the ranges (you won't be able to
reproduce) because the problem consists on the column 1 creating a new
range (because it is hidden, and next logical column != column + 1, 0
+ 1 != 2).

Proposed patch:
http://media.ereslibre.es/2008/10/qtreeview-selection-columns-hidden.diff

Test case example:
http://media.ereslibre.es/2008/10/qtreeview-bugcase

diff:

diff --git a/src/gui/itemviews/qtreeview.cpp b/src/gui/itemviews/qtreeview.cpp
index d5ca633..b7975be 100644
— a/src/gui/itemviews/qtreeview.cpp
+++ b/src/gui/itemviews/qtreeview.cpp
@@ -3494,7 +3494,7 @@ QList<QPair<int, int> > QTreeViewPrivate::columnRanges(const QModelIndex &topInd
current.first = -2; // -1 is not enough because -1+1 = 0
current.second = -2;
foreach(int logicalColumn, logicalIndexes) {

• if (current.second + 1 != logicalColumn) {
  + if (current.second + 1 != logicalColumn && !header->isSectionHidden(current.second + 1)) {
  if (current.first != -2) {
  //let's save the current one
  ret += current;