While this problem clearly is caused by the valve reinforcement region of the tube not falling readily into the rim cavity, I think that there are many variables as to why.

Firstly, the width of the tire being much wider than the inside width of the rim. I seldom see this problem with narrow tires on narrow rims, even when Shraeder valve tubes are used.
The problem then is that the tube inflates with tension inside of the tire, followed by the tube then expanding into the rim cavity.
This causes the tube to be dragged around the inside corner of the rim cavity, which creates high frictional forces from the combined contact pressure and the sharp angle that the tube is being dragged past. Note that the inside corner angle is much sharper when a wider tire is used on a narrower rim.
Obviously, the localized stiffness of the tube reinforcement patch around the valve stem creates even more contact pressure and greater difficulty with this part of the tube dropping into the rim cavity from pressure alone, especially as the reinforced area is both reluctant to bend and reluctant to stretch. Thus, the adjacent, normal-thickness part of the tube simply ruptures as it is pushed toward the rim floor and pulled away from the stiff, elevated reinforced area.

While several of the above recommendations of others are pertinent, such as clearing the valve hole, tugging on the valve stem and using talc powder as a lubricant, I also always have seen this situation improve with the use of a larger inner tube, or, quoting FB: "... I suggest buying the largest tube that fits the tire, so it stretches less, and has more reserve for the added stretch at the valve area....).

FWIW, I usually tug on the valve stem before inflation, and once during inflation (at ~20psi), when airing up wide tires on narrow rims.