It seems to me that if you tell a secret to an ESTP they bring it out to light in a flashy manner and if you confront them they make it look as if the secret is no big deal at all.
As for ENTPs they give you their word yet have to bring it up sometime in a conversation and when you confront them they then give you their word that those other people won't tell a soul.
They both also tend to be very curious about the secret you are keeping and will stop at nothing to find out.
They are pretty much the only two personality types I think have a problem with keeping a secret but some of the IXFPs may let other people's secrets out to their close friends quite easily although if you are telling them your secrets you are probably their 'close friends'.
An incurable scar of life had been put on me because of a problem I had with an ENTP for not being able to keep a secret. I never told a secret again since then.
Anyone else had a similar problem with secret keeping friends? Any other types find it hard to keep secrets?