I've selected logo of vendor but it doesnt display, is that normal ?

Absolutely ! When you create a vendor and you select a picture, you need to save once in order to see the file you chose as the logo, to be sure you have to click on the "Save" button so you can see the logo in the edition list of your vendor.

Concerning the vendor creation from invoice edition, you wont be allowed to add logo, you will must modify the concerned vendor from the "Vendor" tab if you want to add him a logo later.