Modifying feature file in fontra overwrites data in all masters

I am updating my variable font using fontra. All my masters have same GDEF and GSUB data but vary in their GPOS data due to varying width weight and slant between masters.
When I try to modify GDEF Data, the GPOS data of all masters are also overwritten by that of the default instance, as a result alignment of marks are hampered in non-default masters

No files, tests, or entry points are named. Start by reproducing the edit to GDEF data with masters that have different GPOS data, then trace where the default master’s feature data is applied. Done means changing GDEF preserves each master’s existing GPOS data and mark alignment.

Written by the indexing model from the issue text.