Solar wand third upgrade slot not working

[cedar girder]

Description and Reproduction Steps:

I have an osmium quality Solar Wand and wanted to upgrade it.
All 5 giants have been freed (as shown in the lower left corner).
I have 3 upgrade slots available.
I managed to fill 2 of them to gold but when I got to the third one I got an error telling me I need to free more giants (lower right corner) despite having the slot available.

Observation (not sure if related): When I was adding artifacts to enchant I got the bonuses consecutively. Meaning I got 5 No Energy Drains in a row, bringing it to Gold, then 5 Swift Swings in a row, bringing the second perk to gold as well. then I got this error.

Additional information: Once I got the error it will not allow me to Enchant the tool anymore (for example if I want to replace one of the previous enchantments with something new).

Game Platform: PC
Game Version: v 1.1 - 1226
Input Mode: Mouse and Keyboard

EDIT: Removed saved game since I guess there's nothing to analyse according to UnholyRandom's reply.

[thorny pier]

I'm not a moderator but afaik there are only two possible enchantments for the wand (at least, now). So even if you have three slots, there is nothing to put in the third one or replace one of the others with.

[cedar girder]

Oh so it's a feature(ish), not a bug. Thanks for the info!