Every time the client speaks to the server, it needs to provide a transaction id (pzTransactionID). Once a commit is made in the database, the server provides in exchange a new transaction id via the pxClientExchange so that going forward the client could use the new one as its transaction id.
I have a feeling you are running to an error like so "2015-11-20 18:03:41,862 [ WebContainer : 10] ( mgmt.base.ThreadUITransaction) ERROR - ERROR: posted transaction id '9143f677524349fe81f16da214216fec' for frame 'pyWorkPage' DOES NOT match record '6f1c6a4cbb8b60b138adc9207a85d32b'"
There are lots of PDN articles and mesh posts that discuss this topic.
You mention that you are facing an attachment issue in 6.3 sp1. Please take a look at this PDN link.