First off, you might want to change the thread title. This is Scott 131, SG 153.
This is just overinking or viscose ink and not doubled. If you look at more examples of this and other values of the "4 cents" surcharges, you will find perfectly neat prints to rough examples. This surcharging was done locally in North Borneo which accounts for that.
The 4c on 50c here is roughly printed/underinked. The 4c on $1 has a "c" from the wrong size font and also has heavy inking similar to yours.