Of course b10576 is released in the insider fast ring, the day I posted :D

imdisk dev Olof already had knowledge of my problem, caused by -p switch.

I modified the batch MakePartImage.cmd to format drive AFTER imdisk created letter, with format command and by passing parameters from -p switch. It is a little more dangerous for sure.
here the modifications of MakePartImage.cmd :

REM Modification for suppress Windows 10 build 10565&10576 error
REM Following 3 lines had been commented, then following 5 lines had been added

REM --------------------Commented------------------------
REM echo Running: imdisk -a -s %MYSIZE%m -m %SPAREVOL% -f !MYIMG! -x 63 -y 255 -p "/FS:%MYFMT% /Q /Y"
REM imdisk -a -s %MYSIZE%m -m %SPAREVOL% -f !MYIMG! -x 63 -y 255 -p "/FS:%MYFMT% /Q /Y" > imdisk.log
REM if errorlevel 1 type imdisk.log & echo ImDisk operation failed to mount !MYIMG!! & pause & goto :unmount
REM ----------------End of commented---------------------

REM ----------------------Added--------------------------
echo Running: imdisk -a -s %MYSIZE%m -m %SPAREVOL% -f !MYIMG! -x 63 -y 255 then only if no error FORMAT %SPAREVOL% /FS:%MYFMT% /Q /Y
imdisk -a -s %MYSIZE%m -m %SPAREVOL% -f !MYIMG! -x 63 -y 255 >imdisk.log
if errorlevel 1 type imdisk.log & echo ImDisk operation failed to mount !MYIMG!! & pause & goto :unmount
format %SPAREVOL% /FS:%MYFMT% /Q /Y >>imdisk.log
if errorlevel 1 type imdisk.log & echo ImDisk operation failed to mount !MYIMG!! & pause & goto :unmount
REM ------------------End of added-----------------------

This is not for modification of easy2boot (bug or undocumented modification, Olof have no idea as MS did not respond to him), but could be added in the faq ?