Duplicate grafting derivations?

In recent months, I noticed some confusing information during the

grafting phase of updating my profiles.

While doing `guix package -u .` on a large-ish profile (119 packages), I

noticed that webkitgtk is being grafted more than once, like this:

------

applying 25 grafts for /gnu/store/fm6a97lzvy765c1hkk9jixrh0xmc1mwi-webkitgtk-2.32.1.drv ...

applying 25 grafts for /gnu/store/j61ikyxngic90mxfg5m2pv3rf6ilpryd-webkitgtk-2.32.1.drv ...

applying 25 grafts for /gnu/store/x1j851j0pphfyqh6hnar8b3b7y9i6cr5-webkitgtk-2.32.1.drv ...

applying 25 grafts for /gnu/store/zcif8i2b5i66nl59nwfckfqa3x8xwg2k-webkitgtk-2.32.1.drv ...

------

It could be that there is a reasonable explanation for this; maybe there

are some variants of webkitgtk that I don't know about. But, I didn't

find them at first glance.

Does anyone know what's going on here? Is this expected?

I tried to reproduce this bug now, because the derivations I mentioned

are maybe a couple months old (I saved that list back then).

However, it seems like grafted derivations are being substituted now...

awesome! When did that happen?

But it's not easy to try to reproduce the bug.