Strange modal-card-head/foot border animation during modal opening

[fabiobulgarella]

When a modal is launched you can see a strange border modal-card-head and foot that at the end of the animation disappear, leaving head and foot without any border bottom/top.

If you look at the default modal on Buefy, there's no strange border animation and the two border are always shown.
I think it looks nicer an consistent on the default buefy component.

Thanks.