Error In Joined Summing Saved Search

I need to know whether I'm doing something dumb here or I'm asking the system for something outrageous! I'm trying to create a customer saved search that will work out the summed transaction amount and compare that to a summed amount that is stored in a custom record. The problem I get is that when I try one of these joins on the search it works perfectly, however when I try and use two it starts multiplying number by the amount of records present. I will try and explain a little clearer :

The search works perfectly when I use SUM on either one of Transaction->Amount (or {transaction.amount} or Facility(a custom record) ->Amount (or {custrecordcustomerid.custrecord.amount}) on their own within the saved search (i.e. as the only formula column). However, when I try and put the two columns onto the same saved search it begins multiplying both values by the number (count) of custom records present for that customer.