Is there a known variety of the Minneapolis, MN precancel with just a single bar? Here's an example. I happen to have two other stamps (both postage due) with the same single bar, so I tend to doubt it is just a printing anomaly.
NOTE: For the record, the letter height is 2.5mm (not 3.0mm which is very similar but apparently yet another precancel type with double bars.)

Any comments will be appreciated. Thanks.