Just joined the forum so apologies if I'm posting this in the wrong thread. I did try and search but didnt see an obvious answer as I scanned through results. Please feel free to redicted me to the proper forum/threads or to note where this question may have been asked and answered.

It is my understanding that when booking changeable ticket (through BA) that if you need to make changes you will pay for a)the change fee and b) any difference in fare (you will not receive a credit for a lowe fare). My question relates to work travel so in one regard I'm not that bothered (as its not my cost):

I had a round trip (changeable) ticket which I needed to modify, the change was made for circa £1500, no issues/questions. I subseqently needed to ammend again and being told that its another £1500, I go online (to check for my own sanity as if the original RT ticket was £2700, I've paid £1500 to change once, this new flight is another £1500 it must be really expensive! However, I see that the new return flight (when booked as part of a round trip) is only £1500 itself, so I question our admin & booking service who note that its due to booking a new one-way ticket (which is around £3500). Is this standard practice? That when changing you're actually booking the cost as a one-way ticket not as part of a round trip journey (which the origina booking was made as)? Primarily interested so I can understand. Thank you!