I recently noticed that under OSX Inkscape behaves strangely with multiple monitors.
I thought I'd broken the installation as when launching Inkscape it opened and then the window immediately disappears.
Fortunately there's a bug that's been filed here:
XQuartz on OS X 10.9 and later: limited support for multi-monitor setups and the workaround is quite easy.
A quick fix is to turn off "Displays have separate Spaces" in the "Misson Control" panel in system preferences.
The downside is you lose the menus on all connected monitors so they just show up on the primary screen but - if you need to run inkscape and see the window this can be done temporarily if you prefer to have the menus on each screen normally.
Whilst I've seen other potential solutions I'm still looking for something more robust that doesn't involve the solution with turning off menus on all monitors. Let me know in the comments if you find a good solution.