email not sent counted towards quota in new pricing billing ?

[solsTiCe d'Hiver]

hello,
I was evaluating the new pricing model using the usage report in the billing history in the dashboard.

There is 100 recipiends free in the new billing
For emails, I noticed that I had a $0.78 in Used columns against a 1.00 in Free columns

So I guess I must have sent 78 emails.
[that's a strange way to display that free quota. Why not 78 used against 100 free ? or $0.0078 used against $0.01 free ?]

When I look at my logs I see:
22 errors : 'The API call mail.Send() took too long to respond and was cancelled.'
54 mails effectivly sent

for a total of 76 call to mail.Send()

So the failed call to mail.Send() are counted against the free quota !? not very fair.

I take extra care to use task queue to send email at the min rate to not exceed the quota limit. Those errors did not happened before.
May be that's because of restriction on number of running instance I set. or other random circumstances...