Guild Wars 2

For some reason, this item will not accept any upgrade, even though there is an unused slot, is this a bug or am I doing something wrong?

Same here. Item not accept any upgrade.

It seems it only accepts upgrades that require no minimum level.

That’s because it has no level requirement. If you want it to accept upgrades that require up to level N, the required level of the item must be at a minimum N. This can only be accomplished with transmutation stones.

Yes, but you’d assume that any levelled upgrade item could be argued to have a higher level than one which doesn’t require minimum level and hence if an item doesn’t require upgrades of any level, then you can go ahead and use all kinds of upgrades on them, not just “un-leveled” upgrades?