My rakeback calculations != affiliates calculations, am I wrong here?

[Kalledrengen]

Hey there! I'm playing at full tilt and I have a rakeback account there.

When I visit the affiliate site that I signed up through to FTP, I think it seems a little odd at some points. I sometimes have -$ in my rakeback calculations on their site. I'm not too familiar on how they do, I just know I'm supposed to recieve 27% of my rake.



I played 274 HU SNG in different buyin lvls:
27x $5 + $0,25 buyin = $6,75
2x $6 + $0,25 buyin = $0,50
8x $10 + $0,50 buyin = $4,00
186x $11 + $0,50 buyin = $93,00
51x $22 + $1 buyin = $51,00

Hu SNG = 155,25 rake

I played 684 hands in $10 NL shorthanded for a total of $10,90 Rake according to PT

For a total of $155,25 + $10,90 = <u>$166,15</u>
- That is a $18,26 difference from what they have calculated

How can it be possible for me to have -$11,50 the 15'th?
Am I missing something here or is my affiliate site doing something wrong?