Mismatch between map canvas and themed map layouts when using some blend clipping options

[DelazJ]

What is the bug or the crash?

Still experimenting with the "Render layers as a group" option...
Given two layers in a group, the green one at the top, and applying the different blending modes available to it, this is what I get (which afaict is coherent with what is exposed in QEP #235):

By default these settings can't render with map themes in layout (see #50391 for report) but there's workaround. Here the map layout with corresponding themes I get (only "mask below" and "inverse mask below" do match):

Note that a simple map (without theme associated) correctly outputs the map canvas content.

Steps to reproduce the issue

A file showing the issue:
blending_examples_correct.zip

Versions

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QGIS version	3.29.0-Master	QGIS code revision	7e2e622
Qt version	5.15.3
Python version	3.10.6
GDAL/OGR version	3.4.1
PROJ version	8.2.1
EPSG Registry database version	v10.041 (2021-12-03)
GEOS version	3.10.2-CAPI-1.16.0
SQLite version	3.37.2
PDAL version	2.3.0
PostgreSQL client version	unknown
SpatiaLite version	5.0.1
QWT version	6.1.4
QScintilla2 version	2.11.6
OS version	Ubuntu 22.04.1 LTS
This copy of QGIS writes debugging output.
Active Python plugins
MemoryLayerSaver	4.0.4
db_manager	0.1.20
grassprovider	2.12.99
MetaSearch	0.3.6
processing	2.12.99
sagaprovider	2.12.99

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response