I was doing some messy amendments on my ticket last December.

As a result JL London reservation team got some of the fare calculation incorrect.

I was charged
Amendment fee GBP 100
Incorrect Price difference GBP 258
Incorrect Price difference GBP 258
Correct Price difference GBP 284

All 4 showed-up in the "Pending transaction", and my available credit was reduced by GBP 900, when the statement was finalised, only 100+284 stayed.

The incorrect pending charges never went through to confirmed purchases, but it took at least 8 days (if not 2 weeks) before it disappeared.