In Insurt there exists a situation that is particularly troubling, and that is when the player enters a portal through a one use block.
You should note that this situation is never presented in the built-in story & levels, but must be resolved because Insurt features a level editor that should not break under any situation.
Now usually this situation wouldn't present much of a problem. In this illustration, the player could simply proceed to the right and complete the level with ease. However, after going through the portal, the player could turn around and attempt to return to where they came from. Trouble is, this previous position is occupied by the now solid one use block. This will cause the portal to send the player back to their previous position, but now this position is also occupied by a one use block.
The player stuck in an infinite portal loop in an older version of Insurt
Older versions of Insurt had various ways of dealing with the problem. In some cases, the player would get stuck in an infinite loop between the two portals. This was a graceful and harmless way of dealing with the sitation, as the user could simply restart the level. However, portals were extremely buggy and a number of different things could result from the probelm, including the player getting stuck in one of the solid blocks, or falling through the ground to their demise.
This wasn't the only problem with portals at the time. They were prone to issues, including bugs when multiple were chained together, or issues where the player could move during teleportation and cause invalid player positions.
Fortunately, all of these issues have since been resolved. Portals are now very dependable, stable, and predictable. The original double sided portal with one use blocks situation will simply cause the level to restart automatically. This problem demonstrates the importance of properly testing game elements in all conditions and situations.