Buggy export png dialog when opening multiple files

[SomeOne]

If I open two svg files from the terminal:

inkscape a.svg b.svg

Then attempt to export them from the "a" window, the "b" window shows with the dialog controls. If I do this repeatedly, I can get TWO dialogs to show in the "b" window (see attachment).

I get the following warning:

** (inkscape:3945): WARNING **: master 0x7ffb4dfb09c0: unable to add object 0x7ffb520b0c60[DialogExport] to the hash. There already is an item with that name (0x7ffb4ec18500).

Closing the "b" inkscape window (not dialog), then attempting to re-open the "a" export dialog again crashes inkscape, or causes the window not to show.

Im using debian testing:

$ inkscape --version
Inkscape 0.91 r13725
$ aptitude show inkscape | egrep '(Version|State)'
State: installed
Version: 0.91-7+b1

[su_v (suv-lp)]

Earlier reports about the same issue:
* Bug #1481719 “Crash when hiding dock with two files open”
  https://bugs.launchpad.net/inkscape/+bug/1481719
* Bug #1499980 “Tool dialogs end up all in one window when opening multiple documents”
  https://bugs.launchpad.net/inkscape/+bug/1499980

They probably should all be tracked in a single report.