I've watched my positions with D4F go way below my stops occasionally and whipsaw above and below several times before being taken out of the position. However, I have generally found that the stop price (or close to it) was honoured even if the current price was quite far on the negative side. I suspect that because they are not tied to the underlying prices, they have some flexibility in deciding to honour a stop even if the price has subsequently gone the wrong way.
With IG Index, I had one trade where their software wouldn't respond to my order to close the position. By the time I got through on the phone, it had gone much further against me. However, they honoured the price I would have got if the software had worked. More proof that they can be flexible when they want to be.
It probably helps that I'm not a punter who is taking money from them on a regular basis.
I wrote to CapitalSpreads regarding the stop being hit late and got this reply.
I can only appologise for the late activation of your stop.
This occured because at the time your stop level was hit all of our
were very busy with incoming trades and did not notice that a whole
stop levels had been taken out in the FTSE (and wall street etc).
they would just reactivate the stop order if the market had bounced
above the stop level, but in this case the dealers have activated all
which were legitimately hit. In your case the March FTSE had obviously
several points through your stop level.
Normally stops are activated pretty much immediately, but because we do
want an automatic computer stop activation sometimes the stops may be a
little delayed. There is a play off here in that many times we do not
activate stops even though we could do so.
In this case your stop was correctly applied but the reporting was,
tardy. As a gesture towards the fact that you could have traded out of
position a few points higher we will credit your account with 10
I hope that this answers your fears please do not hesitate to contact
you have any further problems.
CEO Capital Spreads