my bank feed transaction won't allocate...now what????

This is the first time i have used the bank feeds to help input my quarterly GST.  I have tried the help line but havent yet got a solution.  When i allocate the transaction and fill and categorise it, once I hit Save, after thinking it comes back up ready to allocate and my previous input of categories is gone.  1/3 of my transactions at least are like this.  Surely this is not how the system works??