Description:
This started happening with latest master.  Did not happen a week ago, or with 6.2.
 
When the attached spreadsheet is opened, clicking in cells does not (usually) move the black selection rectangle.  The row/column headers highlight as expected, but the selection indicator stays stuck on the wrong cell.

Meanwhile, some of the buttons are "buzzing" (vibrating) as if being repeatedly re-rendered at high frequency.

This occurs with macros disabled, so it can not (hopefully) be due to macro code.

Steps to Reproduce:
1. Open attached spreadsheet (buzz.ods)
   Do NOT enable macros.
2. Open tab _PROTO (should already be open there)
3. Click in some empty cells, eg. G16 and nearby

Actual Results:
The cell is selected, but the black rectangle indicating that it is selected does not appear, or appears on some other cell (stuck from it's previous position).

The buttons in the upper left (labeled "MO, <EffPr", "B-W Net" etc.) are vibrating rapidly.

Expected Results:
Selection working properly; buttons able to pass DUI tests.


Reproducible: Always


User Profile Reset: No



Additional Info:
New problem; does not happen with master from last week, or with 6.2.1

Version: 6.3.0.0.alpha0+
Build ID: 32b85ec64e5c901369ce3ce5dbda0e96f2ec7fc0
CPU threads: 12; OS: Linux 4.15; UI render: default; VCL: gtk3; 
TinderBox: Linux-rpm_deb-x86_64@86-TDF, Branch:master, Time: 2019-01-07_16:08:14
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Calc: threaded