Its normally a glitch in the data stream. Or a MM or similar putting in a spurious price.
If you are in contention for the no.1 space then I understand changes can be made to your portfolio. If not then treat it as a learning excercise that tight stop losses cause trades you might not want. This is especially true at market open, you will see many trades on portfolios around 8:20s where opening volitility has caused stop lossses to triger.
Sorry for the delay in replying, missed your post. Thanks for the explanation SMHarman - that's quite true. But in addition I've looked at the trades on ADVFN and the bid offer at the time was 45.0/47.5. So if you put a sell stop at 45.0, the way the current system works is that if the bid hits the amount - which it automatically did as soon as you made the trade it will sell immediately.