Hi,
Ah yes. When you click on the "process" button (or with the preview of the number of results of the filter), the filters are run with a MySQL query on all the products in the shop. However, when the mass action is run through triggers, the filters are run in PHP directly on the data sent by the trigger.
And with the MySQL query, the comparisons are done case insensitive (it's usually the case in MySQL databases to configure the tables to be searchable that way).
However, with the PHP check, it's done with a case sensitive check.
Changing the way the MySQL check is done won't be practical / easy and I don't think we want to change the PHP check to make it case insensitive. So I don't think we'll change the way it's done for now, but I agree that it's a bit misleading in cases such as yours.