Merge pull request #1492 from AvaloniaUI/fixes/1094-spurious-button-press

Fix spurious button presses.

src/Avalonia.Controls/Button.cs

@@ -245,7 +245,7 @@ namespace Avalonia.Controls
         {
             base.OnPointerReleased(e);
 
-            if (e.MouseButton == MouseButton.Left)
+            if (IsPressed && e.MouseButton == MouseButton.Left)
             {
                 e.Device.Capture(null);
                 IsPressed = false;

src/Avalonia.Controls/DropDown.cs

@@ -164,6 +164,7 @@ namespace Avalonia.Controls
                 else
                 {
                     IsDropDownOpen = !IsDropDownOpen;
+                    e.Handled = true;
                 }
             }
             base.OnPointerPressed(e);