Dialogs off-screen for multi-monitor setup

I use a multi-monitor setup with one portrait and one landscape oriented monitor. My monitor
arrangement looks like this:

+------+
|      | +----------+
|      | |          |
|      | |          |
|      | +----------+
+------+

I run Source Tree on the right monitor in full-screen mode.

When I try to delete a file from my working copy in the "unstaged files" list, the warning dialog that pops up is positioned outside the visible area of my screens, above the upper edge of the right monitor. I can only see the lower button row, but not the text of the dialog. (See attached screenshot of uppermost part of right monitor)

I assume this would happen in other heterogeneous monitor arrangements as well, and potentially with other dialogs.