Fernando,
I have such a similar spear haft on a spear. Still I think it isn't shortened with a saw, maybe with a file or something like that to flatten the bottom of the haft. And maybe some less smarter person rubbed with it on a stone. On the picture I wouldn't say it is a fresh saw cut. A saw cut is more smoother and cleaner.
http://www.vikingsword.com/vb/showthread.php?t=1672
Take a look at the third spear. Not a very sharp picture, but you can se that the haft is similar to yours.
To call this a tombak? I'm not very sure, but I think a tombak is something different. I would prefer to call it a lance or a spear with a good forged steel blade.