Do you confirm that the <use_enriched_content_type> flag is important and that with <use_enriched_content_type> set to Y your testcase works also in Server 5.1.2 ?
Yep.

In fact, we notice that in the configuration you sent the <use_enriched_content_type> is N.
So, can we assume that, by moving from 5.1.1 to 5.1.2 (which is straightforward) and setting <use_enriched_content_type> to Y, you have fixed your issue, as far as your operativity is concerned?
Locally yes. I'm trying to avoid server upgrades because our deployment scripts are ... less than fully understood.

Do you mean that with Server 6.0.3 your testcase works even when <use_enriched_content_type> is N?
I just checked again to make sure. Yes.

According to the logs included in your testcase, we see that the testcase still involves an OSX client library 2.0.1 trying to connect to a Server 5.1.2, which is not supported.
Is this the extension to 5.1.2 that you would like to be applied?
That's the behaviour I would like to test, yes, thanks.

Since the Flex client connects, but the iOS/OSX one doesn't, I thought I might be looking at a client bug. It sounds like this isn't the case. On the off-chance that it is, then a fix would be great, otherwise screw it, I'll get the wheels turning for an upgrade.

Thanks to both of you by the way.