[GNC] 'End of Month' always sets Bill due date to end of *next* month

[Adrien Monteleone]

I have several vendors where payment is due at the end of the current 
month of the date of their Bill to me. It doesn't matter what day of the 
month I select. The result is always that the Date Due is set to the end 
of the following month. (note, I found an old RFE to add this very 
behavior, but its status was still not closed: 
https://bugs.gnucash.org/show_bug.cgi?id=670215, so not sure if any 
action was taken, or just an oversight to close it.)

I'm sure it is something I'm setting incorrectly, but I can't quite 
figure the culprit.

This Billing Term is currently set as:

Type: Days
Due Days: 30
Discount Days: 0
Discount %: 0

(Note, if I enter a bill dated the 7th, it doesn't set the Due Date 
30-days hence. It sets it as the 30th of the *following* month, which I 
find odd on its own, especially since I also have Net30/60/90 terms 
defined with the same settings, and those work as expected--30/60/90 
days hence)

I'm sure the Due Days setting is the culprit, but when I look at 
changing it from type:Days to type:Proximo, it gets more confusing:

Due Day:?? (supposed to be the day of the month bill is due, but that 
isn't a static number)
Discount Day & % aren't relevant to me here.
Cutoff Day might, but I think I want it at '0' because I always want 
this to be the end of the 'current' month. (at least so far, but this 
would help if I have a case for 'end of next month' terms.)

I did a trial setting Proximo, Due Day: 30 and Cutoff: -1, but that 
didn't work either.

Ideas? Suggestions?

-----
Also, I tried to delete the Billing Term and re-create it, but it tells 
me it is in-use. There are no pending, non-paid documents using it, but 
I suppose it applies to any historical document. (not sure why since it 
is 'finished with') Unfortunately, I don't see a way to find *which* 
documents are using that Billing Term, so I have quite the haystack to 
sift through. (though perhaps some crafty 'find' on the XML file 
directly might do the trick)

Regards,
Adrien