In OPC UA 1.04, it was very explicit that Strings are not null-terminated:

All String values are encoded as a sequence of UTF-8 characters without a null terminator and
preceded by the length in bytes.

In OPC UA 1.05 the waters have been muddied and now additional behavior that is "not guaranteed to be interoperable" has been allowed:

Strings with embedded nulls (‘\0’) are not guaranteed to be interoperable because not all DevelopmentPlatforms can handle Strings with embedded nulls. For this reason, embedded nulls are not recommended. Encoders may encode Strings with embedded nulls. Decoders shall use the length to read all bytes in String, however decoders may truncate the String at the first embedded null before passing it on to the application.

I cannot wrap my head around this decision. Now my stack, which decodes Strings to spec as of 1.04, suddenly looks like the broken one when some other server out there is using null-terminators in Strings as if they are significant. To make matters worse, UaExpert, or the underlying stack, truncates Strings at the first null byte, which further complicates the issue because now everyone thinks null terminators are significant and that's the correct behavior.