please help how this configuration is working

hello,
As my question is related to linux and c posting it at C and
networking forum. I took two linux PCs then does some changes that
always packet to
Ethernet layer have length 1510 thus completing frame length as 1524
instead of 1514 by crossover connecting both pcs.
then i did FTP and try to get and put 50MB file. The changes are
done after packetlen > nextpcMTU thats why i am able to bulid 1508
packet.
FTP works well when i try to get file on PC1 from PC2 but when i
try to put same file from PC1 to PC2 it will looping in sending file
and does not complete its task thus allowing me to terminate FTP
Whats happening here? i am not getting?
regards,
rahul.