Level editor bug; entities disappear when map is loaded

[AlexxShadenk777]

I wanted to have shirts of different colors, so I tried what I could muster on my own. I copied the hanging_shirt_white entity, edited the texture *.dds to the color I wanted (blue for starters), then finally I renamed every instance of the word 'white' with 'blue' (among other colors after editing the color of the texture), and that goes not just for the filenames, but also edited inside the *.ent, *.dae and *.mat files with notepad. I also changed the path inside *.mat so that it fits the path of the custom story I'm working on, to load from the custom_entities folder inside it.

Everything worked, I could load all the shirts I edited into the level editor without any errors, so I saved the map, and tested it in-game. It didn't crash so I rejoiced.

But here's the bug. After closing the editor, then opening it again, when I load the map with the edited shirts, I get an error message and all those shirts aren't loaded anymore.
"Found some errors while loading file. Check log for details. File index out of bounds!" it says.

Either I keep the level editor until I'm absolutely finished editing this room (and by extension the PC), or something can be done to prevent this from happening again. Or is that normal when loading custom entities outside the default folder? Cuz I'd rather keep it like this, so that when it's finally released, I can pack up just the custom story folder instead of having to fumble around with extra folders and such that will land in the root directory when unpacked.