A request to calculated composite values is sent to the server after any input changes. When the request is returned, the values of the composite tests are updated.
If two (or more) values are entered rapidly it will send off two requests within a very short time period (say ReqA & ReqB). Although it should be very rare (e.g. I haven't seen it yet in the past few years!), there is the potential for reqB to return before reqA. This would mean that first ReqB would set the composite values and then reqA would overwrite them. Since reqA was based on an earlier input state it's composite values are now out of date (reqB's are correct).
The easy fix is to abort any existing composite calculation before a new one is fired.