When holding a widget like button for example in the widget editor it keeps growing.
It keeps growing infinity if you hold it down works with all widget things.
That’s just from me holding it in 
i can make video to prove it if needed!
Seems like some background weirdness. Doesn’t break anything and the name is reset to the index it had when you picked it up once you release the widget. 4.18
Not sure if that’s a bug. UMG always adds indexes but his behaviour is a tad strange, true.
If you’re truly concerned:
https://epicsupport.force.com/unrealengine/s/
I must admit I’ve never seen this before in action. Still present on 4.20.1. It might have been here since UMG was introduced, tbh.