Mined cow spawners, hologram left behind (unsure if more serious issue)

I had 2 cow spawners placed, I mined them (mining while sneaking, to pick up the stack as 1 item) and it left this hologram behind. No idea if this will disappear on server restart. See screenshot Reporting as Major only as this may or may not indicate some much more serious issue (I.e. would those spawners have not counted towards F top?), no idea. I did try placing a core after and it does seem to correctly count my number of spawners after I broke this. I was not able to replicate this issue but the hologram is still there as of making this report.