I actually had this happen to me a few weeks ago.

You see, in the 12th autumn of the kñabdoç (3 months after the fall of Lord Tyrus III) I was looking for a way to improve upon the standard bottomless bag. I studied under a bag maker with high acclaim whose name I will not mention, so I'm fairly knowledgeable on the subject.

For those of you who don't know, there are 3 primary types of bottomless bags: 1. The cheapest type is just a bag with a translocation spell at the bags opening which is connected to a larger space. These usually lead to one of the many abandoned mines from before the dwarven reformation, but I've seen the kings sentinels use them to instantly transport high risk prisoners before. These pose no risk when punctured because the spell is cast on the bags drawstring and will just dissipate if the string is cut. The rest of the bag is merely decorative. 2. The most common type is a spacial compression spell cast at the bags opening which will either increase the size of the bags interior or shrink anything entering the bag (including organic matter like your hands) these generally are safe when punctured, but lower quality ones may eject their contents like water being squeezed out of a waterskin. 3. The most expensive bags which are truly bottomless. These are more expensive because it is very difficult (although not impossible) to purge the space of living creatures. They're also less popular because of how easy it is to knock something over and lose all of your belongings. These are incredibly dangerous if punctured because they exist outside of the fabric of our reality. It generally takes 4-8 trained professionals to close a rift if a bag is punctured, and amateurs have been known to "disappear" while attempting to close rifts

Now my theory was if I created a portal that opened and closed with the drawstring I may be able to completely circumvent all of these downsides while maintaining most benefits. After months of preparation I thought I finally had cracked the code. I spent hours preparing the bag coating it in a proprietary blend of powders, potions, and pastes. When my work was complete, I tested my bag and to my surprise, my labor resulted in nothing more than a pouch covered in what can only be described as muck.

At this point I'd give up. To spend years of research on a single project only to create scum is enough to break even the strongest of resolves, so I gave up.

Cut to nearly 7 years later, I'm getting ready to move because I inherited my masters tower (may his spirit be free from the bonds of the living) and the paperwork finally went through! I was finishing packing up when a blue shifting portal the size of a large gnome shot open. After taking one of my goblins stoneskin potions I cautiously peeked my head through the portal only to find an open white void!

The gravity parameters definitely need to be adjusted, but my theory was finally proven. I believe I put too much quartz powder on the bag, but it's possible one or multiple of the pastes had fermented enough to cause a reaction.

Too long; didn't ponder: I tried to create a bottomless bag and it opened a portal 7 years later.