Lookup Sorting


I am using FontForge.
I have a feature while there the rligs are sorted by the number of combinations.
Glyphs with higher combination comes at the top and the one with less combination goes down in the list.

When I am merging the feature file using File ->Merge Feature Info, merging happens fine but when I check the Lookup, I find that the sort order is lost.

There are few thousand ligatures. Its an Arabic Font.

How do I keep the order of feature file?

Please help.