localConnection and the localhost

I have had some success using LocalConnection between SWFs.
I can have a connection function between a preloader SWF and its child, and another connection work between two SWFs present on the same webpage…most of the time.

If I run my SWFs in a webpage from my localhost (ie my local testing PC) a particular LocalConnection will fail about 50% of the time. If the same SWFs are run on a remote server (ie the inernet) the LocalConnection works 100% of the time.
SWF ‘A’ is sending to SWF ‘B’
Bizarrely, the LocalConnection going the other way, from SWF ‘B’ to SWF ‘A’ works 100%.

All the other LocalConnections I have used all work 100% of the time.

I have tried adding a listener to the eventStatus which reports when the connection fails.
I have also tried allowDomain(), although Im not sure it is neccessary since all the SWFs are
hosted from the same domain anyway.

Why should a LocalConnection behave differently depending on where the SWFs are hosted?