[REGRESSION] Moving an object behind another object works only after reopening a project

Requirements

• I searched through the issues if the issue already exists

Steps to reproduce

1. Create a histogram.
2. Add e.g. a reference range.
3. Move the reference range behind the histogram.

Expected

If you move an object behind another object (in this case the reference range behind the histogram), it should be immediately displayed behind the other object.

Observed

The object being moved behind another object is indeed displayed behind that object but only after reopening a project file. Otherwise it is still visible in front of that other object.

LabPlot Version

Debug build 
System: Ubuntu 24.04 LTS
Locale: English,United States (Decimal point ',', Group separator ' '
Number settings: Decimal point ',', Group separator ' ', Exponential 'e', Zero digit '0', Percent '%', Positive/Negative sign '+'/'-' (Updated on restart)
Architecture: x86_64-little_endian-lp64
Kernel: linux 6.8.0-35-generic
C++ Compiler: GNU 13.2.0
C++ Compiler Flags: -g -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -fdebug-prefix-map=/build/labplot-6MoFl1/labplot-2.10.1+git202406200147~ubuntu24.04.1=. -flto=auto -ffat-lto-objects -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -Wdate-time -D_FORTIFY_SOURCE=3 -fno-operator-names -fno-exceptions -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -Wall -Wextra -Wundef -Wpointer-arith -Wunreachable-code -Wunused -Wdeprecated-declarations -fno-omit-frame-pointer -fstack-protector -fexceptions -std=c++17 -O2 -Wcast-align -Wswitch-enum -fvisibility=default -pedantic -Wzero-as-null-pointer-constant