Gpencil : join and keep animations layers

when i want to join 2 GPencil objects ,eventyally every object have its animations data and every layer in both objects have its animation data. i expect to have the animation of the active Gpencil object(no problem here) and all layers with in both object must be kept (no problrm untill now), the issue here is all layers of active Gpenil object have their propre animation with all the groups channels created and their f-curve modifiers but layer of selected joined object lost all animations (on transform, opacity) and all Groups channels and f-curve modifiers ....so all Effort go away in addition all modifiers that related to those layers are gone (ie:restricted by layers are gone)

i hope to support in having 'join and keep all' operator and also