This is probably a legacy bug from the original game, but as I haven't used the spell earlier, here’s the report:
Current behaviour: when you set your mage to cast Enchanted Weapon and then switch your focus to another party member, if the mage finishes the spell while not being selected, you don’t get to select the weapon to create. No weapon’s created, thus the spell is wasted. Also the bottom menu bar of the currently selected character becomes blanked out as an effect of the spell (reselecting or clicking on the bar fixes this) - it’s probably an attempt of the game to present the four options for the weapon to be created, but, as I said, no icons appear for this.
Expected behaviour: upon completion the options are shown, no matter which character is currently selected. OR the spell effect could be changed so that instead of in the bottom bar, it displays the options in a window similar to the sequencer spells. Those currently work without problems, regardless of the selected character.