As noted by Keith Avery in his comment, the ListAll classmethod of %SYS.Namespace may also include implicit namespaces. This is mentioned in the class doc. I haven't verified, but I guess that you may get different results from ListAll() if you run it once immediately after Cache startup and again after Portal has been used to change namespace definitions (e.g. mappings).

ListAll() is implemented using calls to the undocumented $ZUTIL(90) function. I dug up some WRC information we received in 2010 about a change in behaviour in that function starting with Caché 2010.2. The summary was:

SML1081 - Support single namespace activation and reduce usage of mapping memory.

Using the extra info from Dinesh, here's what I did to investigate. Admittedly I was on a 2015.1.0 Ensemble on Windows, but the classes are unlikely to have many differences between this and his 2015.1.2 on Solaris.

First I cleared the read-only flag on the CACHELIB database that stores %Net.HttpRequest:

Then I loaded the class into Studio (for safety I set the read-only checkbox during opening), compiled it, used the View\View Other Code option (Ctrl+Shift+V) and jumped to the line of the error Dinesh reported.

I reset the "Always Mount Read-Only" checkbox on CACHELIB, to prevent accidental changes.

In the code several things caught my eye:

 

Maybe disable the GZIP feature on your SOAP adapters and see if the problem persists. Searching the InterSystems doc for the term GZIPOUTPUT may give you clues (I'm no expert in this area).

I also recommend you ask InterSystems Support (WRC) for help on this, particularly as you're running on a less common platform (Solaris).

That's interesting Jeff. I wonder if you were on the "Developer Community FAQ" page of DC when you clicked the "Create New Post" button? If so, it looks like that'd pre-populate the tag field in the way you reported. @Evgeny Shvarov, maybe this case could be treated as an special case by the DC software, stopping it from proposing the "Developer Community FAQ" tag.