The problem is this: when the resulting icons are used in the resource file, you would need to include project.mbg in project.rss. But the .mbg file is generated after the resource file is compiled, as this is the practice when using makefiles. In this case the makefile's RESOURCE : label is called after the rsg file has been created.
There is a way around it, which is generating the mbg file earlier, using the LIB : label instead of the RESOURCE : label host the mifconv statement.
Because LIB is called before RESOURCE, the mbg file will be build now for before the resource file.
The is still a caveat: only "abld build" will now work properly all the time. People who did "abld resource" will still find their mbg file out of date. It is also not possible to do mifconv in both LIB and RESOURCE, as this will lead to the mbg file alsways being younger than the compiled resource files.
The only long-term solution is to have mifconv being part of the regular mmp file syntax.
Finally, I only saw this after the mbg file was deleted. This resulted in make not being able to see the project.mbg file at all and aborting the entiere build. If the mbg file was left over from earlier bmconv builds, this problem would have been hidden.
Sander van der Wal