What I'm actually trying to do is to elaborate [this question][1]. I'd like to use `Pane` with scrollbars enabled to explore large (sparse) matrices like this one:

![enter image description here][2]

Here is what I have so far using some ideas from [this answer][3]:

    A = ExampleData[{"Matrix", "HB/west0381"}, "Matrix"] // Normal;
    {n, m} = Dimensions@A;
    mp = MatrixPlot[A, ImageSize -> 9 m, Mesh -> All];
    DynamicModule[{trans, ij, mpos},
     trans[{x_, y_}] := {Clip[Floor[n - y] + 1, {1, n}],
       Clip[Floor@x + 1, {1, m}]};
     Pane[
      Show[mp, ImagePadding -> {{40, 20}, {20, 20}},
       Epilog -> Text[
          Framed[
           Dynamic[(ij = trans@MousePosition["Graphics", {0, 0}]) -> 
             A[[Sequence @@ ij]]], Background -> White],
          Dynamic[MousePosition["Graphics", {0, 0}]],
          {1, -1}
          ]~Style~Larger
       ],
      {500, 500},
      Scrollbars -> True]
     ]

The result is

![enter image description here][4]

-------------------

**Now about the problems**
 
 
**1.** The main trouble is that it does not correctly translate coordinates
for horizontal scrolling. If we don't touch the horizontal scrollbar
everything is fine:
        
![enter image description here][5]
        
But if I slide horizontally the label shifts and falls outside the
visible area. It looks like a Mma bug.
  
**2.** The second funny thing is that if I remove `//Normal` from the first row then   `MatrixPlot` produces the following:

![enter image description here][6]

  which seems to be the second bug.

**3.** And finally the issue which is due to my confusion with `Dynamic` things. In the code I use `MousePosition["Graphics", {0, 0}]` twice (can this be the reason for the item 1 from above?). When I tried to save this coordinates in a variable I had no luck. But there must be a way to do this.

----

Any suggestions?
  [1]: http://mathematica.stackexchange.com/q/2512/219
  [2]: https://i.sstatic.net/X6rNA.png
  [3]: http://mathematica.stackexchange.com/a/2524/219
  [4]: https://i.sstatic.net/SLaS3.png
  [5]: https://i.sstatic.net/RP8aZ.png
  [6]: https://i.sstatic.net/JIChf.png