@hellnbak said:
.......... But, what I'm looking for is an explanation of why it happens, and how to make it not happen anymore.
......
Hi, attached file / model may somehow explain what is going on when creating similar weird faces.
There are certain "conditions" that have to be met to create them. Don't ask me why SketchUp can't handle them. It probably has to do with the order of creating loops and the sequence of edges and their endpoints that confuses the program to decide which faces have to be created and where to split them. The model shows two situations that you better avoid when modelling. Although dragging endpoints accross an opposite edge isn't the most likely operation.
Often "intersect faces with....." doesn't help. And you can keep on adding edges, only shifting the profiles to some other little face. Delete the corrupt part and/or re-create it with a workaround (like in the second scene)
I hope this somehow helps in understanding when and why this issue occures.
weird faces