[eclipse-dev] inconsistent drag-n-drop to create split-window in Neon+GT

[pgndev <pgnet.dev@xxxxxxxxx>]

I'm running Eclipse Neon (build id 4.6.0.I20160517-2000) on linux/64.
It's running under GTK3, launched as 'SWT_GTK3=1 eclipse'.

I'm seeing some IDE 'glitchiness' on dran-n-drop to split-window.

I'm neither sure how to debug this, nor which relevant component to
post a bug under.  Pointers/suggestions appreciated.

Here's, generally, what I'm seeing:

In any editor, open multiple documets.

Grab a tab-handle, drag to any editor window.

With earlier installs, on drag, a split-window separator would
instantly/consistently pop-up.  On drop, a split-window would be
created along the last visible separator's boundary.

Currently, it's still possible to create the split-window, but the
sensitivity is coarse, at best.  You have to move the mouse/pointer
around (can't yet determine the trigger, or the pattern), in order to
get the separator to popup in the first place.  Then, on drop, the
split-window's not always created.

A couple of repeated attempts does the trick.

Is this a known issue?
What component is this most-likely under?
What additional info's neede to troubleshoot further?