This causes basehash mismatches:

    python () {
        if d.getVar('USING_WIC'):
            fstypes = d.getVar('IMAGE_FSTYPES').split()
            basetypes = set()
            for fs in fstypes:
                # Add the basetype to our set of basetypes in use
                t = fs.split('.')[0]
                if t != "wic":
                    basetypes.add(t)
            d.appendVar('IMAGE_TYPEDEP_wic', ' %s' % (' '.join(basetypes)))
    }

This seems to work without issues:

    def get_workaround_wic_typedeps(d):
        if d.getVar('USING_WIC'):
            fstypes = d.getVar('IMAGE_FSTYPES').split()
            basetypes = set()
            for fs in fstypes:
                # Add the basetype to our set of basetypes in use
                t = fs.split('.')[0]
                if t != "wic":
                    basetypes.add(t)
            return ' '.join(basetypes)
        else:
            return ''

    IMAGE_TYPEDEP_wic += "${@get_workaround_wic_typedeps(d)}"