Bisect Not Accepted - Postage Due 1/2¢ Or 1¢? Or 1 1/2¢?

Just came across this in a shoe box I forgot about As of April 15, 1925, third class mail was 1 1/2¢, so why the notation "due 1¢"? Presumably only the bisect was not accepted or was there some sort of penalty for philatelic mischief?. Or was the entire franking disallowed and the total postage due was 1 1/2¢? The handwriting and the circling of the 1/2¢ stamp look to be done by the same pencil??

Of course very lucky for me that the postage due which was actually applied was 1/2¢

Postage due here was double deficiency, so when the bisect was not accepted it should be 1 cent due. The PO clerk should have known that, so I wonder if this was possibly a friendly over the counter deal.

Thanks much for the info!

Since single use of a 1/2 cent postage due stamp (alone) on cover is a highly desirable item there is always the possibility of manipulation. The postage due stamp does not look properly tied to the cover. Many postal clerks "precanceled" sheets of postage due stamps to save time. Your postage due stamp could be one of these with a crude attempt to tie it to the cover. Again, this is based on looking at a scan and I may be missing something.

That crossed my mind also, but the postage due stamp is circled in pencil, so something was affixed there. I suppose someone could have replaced a one cent postage due stamp with a 1/2 cent one, but that seems rather nonsensical since the "due 1¢" is so prominent.

Surely this is a correct usage of the half cent postage due stamp as it indicated the half cent deficiency... why issue a half cent postage due stamp if there was no actual coin of that denomination to pay?
I'd say the stamp indicated the amount due for the deficiency and the pencil "due 1c" added a half cent penalty.