ImageMmosaic 2.13.3-2.15.0 transparent area overlaps with other geotiff making blank space

Description

Hi,

this is a copy of:
https://gis.stackexchange.com/questions/313758/geoserver-2-13-3-2-15-0-imagemosaic-blank-transparent-spaces-with-overlapping
and
http://osgeo-org.1560.x6.nabble.com/Geosrever-2-13-3-2-15-0-ImageMosaic-overlapping-transparent-from-alpha-band-td5397109.html

I'm migrating from OracleJDK1.7/Geoserver2.8.3 to OpenJDK11/GeoServer2.15.0,
and have issues with ImageMosiac layers. In short words - can't configure
two geotiffs to glue together where they overlap.

Tried and searched everything, installed 10 versions of Geoserver and
figured out it stopped working in Geoserver 2.13.3 (GeoTools 19.3). In
GeoTools release notes I found that some transparency issues were fixed
then, but it stopped working for me.

I understand that I have alpha band in my files, not "no data" so popular
problems with no-data and enabling JAI-EXT, setting transparency color is
not the problem/solution.

It works fine with no configuration (just clean geoserver install, create
store and publish layer, only set names) with JAVA8 / Geoserver 2.8.3,
2.12.5., 2.13.0, 2.13.2 but not 2.13.3 and next releases.

Attached sample tiffs

Environment

Ubuntu 15.10 + JDK8 + Tomcat 8 + Geoserver 2.13.3
Ubuntu 15.10 / Ubuntu 18.04 + OpenJDK11 + Tomcat 9 + Geoserver 2.15.0

Status

Assignee

Unassigned

Reporter

Łukasz Bocianiak

Triage

None

Fix versions

None

Affects versions

Components

Priority

Medium
Configure