Another surprise, on AROS x86 I used "processicon" to change the icon type and also this program behaved the same as "seticontype", practically works with all icons except DualPNG.
Now comes the surprise, I tried to create the DualPNG icons on OS 4.1 with the same program "IconEditor" that I normally use on OS3 and AROS 68k, well, the DualPNG icons created on OS 4.1 is possible to change the type to the icons with both "processicon" and "seticontype" that I had compiled.
So on OS3 the DualPNG are generated differently than on OS4 even if all OS see them perfectly.
There is an answer to all this, the developer of "IconEditor" when he compiled the 68k version of "IconEditor" told me that on OS3 something was missing to be like the OS4 and MOS version, "now I don't remember what".