Hi Andrew,
I am afraid, I am unable to reproduce this issue in v.4.1. Please refer to the sample attached below and let me know if you are able to reproduce this issue in it. The merging process works fine in the sample.
Please check whether you have given the
MergeOrder value correctly.
Thanks for using Syncfusion products.
Regards,
Mano
Menus_merging_41217.zip