CMake performance difference: --build --preset vs. --build dir - performance

Question

I have a CMake solution with ~1.5K C/C++ projects/subdirs and I wanted to use CMake presets. This is my CMakePresets.json:
{
"version": 3,
"cmakeMinimumRequired": {
"major": 3,
"minor": 20,
"patch": 1
},
"configurePresets": [
{
"name" : "base" ,
"displayName" : "Base Config Preset" ,
"description" : "Base config using VS2019" ,
"generator" : "Visual Studio 16 2019" ,
"architecture" : {"value":"Win32", "strategy":"set"} ,
"binaryDir" : "G:/.bld" ,
"installDir" : "G:/.dst"
}
],
"buildPresets": [
{
"name" : "base" ,
"displayName" : "Base Build Preset" ,
"description" : "base build preset" ,
"jobs" : 0 ,
"cleanFirst" : true ,
"verbose" : false ,
"configurePreset" : "base"
}
]
}
I observed a significant duration difference (~40%) between the following 2 approaches (both were run in an identical clean context):
Using classic folder syntax to build
cmake --preset=base
cmake --build G:\.bld -j
Using new preset syntax to build
cmake --preset=base
cmake --build --preset=base -j
Both perform similar during CMake config & generate step. The difference appears during build step, after the Microsoft's header is displayed:
Microsoft (R) Build Engine version 16.11.2+f32259642 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.
Approach 1. does not have any delay until it displays the following output lines. Total time is ~14 minutes
Approach 2. has 5-6 minutes delay before showing next lines from output (but the CPU is under load). The Microsoft's header is displayed again then everything continues normally. Total time is ~20 minutes
The duration difference seems to be, more or less, that initial delay, when nothing is displayed
Shouldn't they be identical?
Could be a bug in CMake or I do something wrong?
OS: Windows 10 64bit, cmake version 3.21.2