Welcome to the community, @Martin_M! :grinning_face_with_big_eyes: One thing to remember about lookup fields is that they contain (and return) arrays. The “is” filter condition is supposed to look for an exact match, but it appears that with an array, it’s currently satisfied to find a match with any one of the array items. I can see the case you’re making, and agree that the comparison should be more precise. I strongly suggest contacting Airtable support, sharing the same info you shared here.
In the meantime, there’s still a way to get what you want with some small tweaks. If you change your field from a lookup to a rollup, you can have greater control over the output, and create something that will work as an exact match for a filter.
The only meaningful difference between a lookup and a rollup is that a rollup lets you specify what to do with the array that it builds. This is done via the aggregation formula field. In your case, the formula could be:
ARRAYJOIN(values, ", ")
This will give you a string that looks the same as the displayed version of a lookup field, but will properly compare using an “is” filter condition.
