When a compiler error or warning occurs in a header file, the ‘Problems’ view gives no indication of where the header was being included at the time.
I guess you mean: “at the first time”? 
Do you know the Include Browser view?
It may be usefull to know what includes what, or what is included by what.
When you have a file opened in the editor, go to Navigate > Open Include Browser.
When the Include Browser view is opened, you can also drag’n drop a file from the Project Explorer to the view to refresh it with this file’s information.
No, I didn’t mean that at all.
I know how to find all the places where a header is included - I meant which specific inclusion of the header is having the error.
The compiler output tells you;
eg, if file1.c and file2.c both include header.h:
But the ‘Problems’ view shows only “error in header.h” - it doesn’t tell you which specific inclusion.
Knowing all files that include header.h is no help here - we need to know the specific inclusion
Obviously, if the header has an error in one inclusion but not the other(s), then it’s something to do with that specific inclusion - hence the need to know the specific inclusion
The information is available form the compiler output - but the ‘Problems’ view discards it! 
Ok I get your point; we will investigate in order to add information in the problems view.
Waiting for this, you can obviously get the information from the console output, by looking for the error string (Ctrl+F when the error view has to focus).
Cheers! 
How much of this is specific to M2MStudio, and how much is “generic” Eclipse behaviour?
Indeed - that’s what I’m doing. 8)
But the console output is sooooooooooooooooooooooooooo verbose! 
GCC error parser is the Eclipse generic one, but we have possibility to enhance it. And we can also post bugs on Eclipse bugzilla 