[Flex] setMask problem in external swf

This is driving me crazy.

Ok, firstly, in the initialise function on one of my objects, I have this line:

this.topview_mc.setMask(this.topviewmask_mc);

topviewmask_mc is a movieclip, topview_mc is a custom object which extends the movieclip class. The swf this is in is being embedded in a flex movie.

The mask isnt working at all and both objects show on the stage. If I comment this line out and set the this.topviewmask_mc layer as the mask for the this.topview_mc layer it works fine, but I would prefer not to do it this way as it’s also happening on some dynamically created/loaded movieclips.

When I get the path values of the two objects I get these:

_root.topviewboard_mc.topview_mc
_level0.flexi_plan.designboards.FlexLoader276.instance349.topviewboard_mc.topviewmask_mc

They are both on the same timeline though.

Any help with this is appreciated.

Thanks,
Brendan.