This option can be avoided unchecking the "Import bookmarks..." in the installation steps.
Doh! I didn't think to that for Portable!
Maybe there is some info in OHelp files.
Well, even Opera Portable from PortableApps creates and doesn't delete those files I've mentioned above, however it writes them in a OperaPortable folder inside Windows TEMP folders. It should be enough not to interfere with Opera Desktop.
Better than nothing.
O.O Didn't know that, despite I've use USB versions from both, Opera and PortableApps and had no problems but didn't check traces on the computers since every file should be deleted from them, at least in every PortableApp.
I'll check it.