Inconsistent substitution string expansion in email templates - SCSM 2012 R2

Question

Coming to the conclusion that email templates should not be stored in a custom MP ?
I'm seeing odd begaviour where only some fields are expanded when the email is created. See below example where ID in the subject line has not been expanded but it has been expanded in the body of the email. If I store the custom template in "Service
Manager Incident Management Configuration Library" then it works as expected.
In the following notification, Subject has not been expanded yet when ID is used in a subsequent field in the email body it is expanded (Fault No.)
Also Affected User Firstname has not been expanded.
Subject: Your call has been closed.  ID: $Context/Property[Type='WorkItem!System.WorkItem']/Id$
Fault No: IR223
Fault Description: Testing Open, resolve & close notifications
Dear $Context/Path[Relationship='WorkItem!System.WorkItemAffectedUser' SeedRole='Source' TypeConstraint='System!System.Domain.User']/Property[Type='System!System.Domain.User']/FirstName$,
Please be advised that this call has now been marked as closed.
Ian Moran

Answer 1

it should be noted that those substitution strings are contingent on the MP that stores the notification template. for example, 'System!System.Domain.User' is only valid if the
MP Reference "System" points to an MP that contains the element System.WorkItemAffectedUser, and that element is a relationship class definition.
to break it down:
$Context/Path[Relationship='WorkItem!System.WorkItemAffectedUser' SeedRole='Source' TypeConstraint='System!System.Domain.User']/Property[Type='System!System.Domain.User']/FirstName$
$ starts and ends a variable.
Context is one of the keywords that control the behavior of the variable, but in this case, you can read it as the target of the notification template.
Path[] means we are going down the projections path \
Relationship modifies path by specifying which relationship to follow in the brackets with the Relationship element.
SeedRole modifies path by setting which side of the relationship the starting objects is on, in this case, the "context" is the source of the relationship.
TypeConstraint filters path based on what's on the other side of the relationship, in this case, it must be a user.
Property[] means we're reading data from a property of this user, as opposed to pathing again
Type modifies property by controling which class to get the property set from
the last entry is the property name to get data from, i.e. the
FirstName property.
Consider http://technet.microsoft.com/en-us/library/ff719642.aspx and
http://msdn.microsoft.com/en-us/library/ee533748.aspx, thou Context is new for service manager and is largely undocumented, I suspect it was added to address related classes, as (also speculation)
Target may refer only to the target entity without its relationships.