Hi Simon,
I have recently had some problems with this issue, possibly caused by the same situation.
I work with Moose in VisualWorks and parse my models with inFusion 7.2.5.
My problem was that I parsed my system in MacOSX and then wanted to use the source browsing in Windows. Apparently, inFusion exports the sourceAnchor with the OS-specific separator, and in Moose the path to the source code file is built by adding (using OS-specific separators) to the sourceAnchor in the model. Since I parsed the system under MacOSX, the sourceAnchor separator was /, and then tried to access the source code from Windows, and what Moose did was to concatenate two strings: src\ModelName\ (containing the Unix separator) with /org/foo/bar (containing the Windows separator), which leads to an invalid filename (in Windows it lead to src\ModelName\orgfoobar...).
The right solution would be to make Moose>>browseSource parse again the sourceAnchor and replace the alien-OS separators with the right one before building the filename for non-Smalltalk entities.