sms texts always in new threads sent and received

hey

i have a wierd problem with texts

every message i receive goes into its own thread instead of updating the current persons text thread..

i just changed rom's so backed up my sms's with sms backup and restore. , after restoring i noticed that all my sent messeges and received messages to people there in 2 different threads for each person one thread for sent one for received....

so i thought it might have been a dodgy backup... so i viewed the backup but everything looks ok nothing is split into 2 threads .... each person has 1 thread

so i thought it might be the sms backup not being compaitable with my new rom (dragon j/b 1.7) so i deleted my sms's ALL of them and started from scratch....

but again i just received a text from a friend i replied to that and when he replied again it went into a new thread......

anyone help?

checked my contacts they are all linked (ie, facebook....google.... accounts into one contact file)