Weird loop cut and slide glitch, just some random inward mesh deformation I've only had the program for a few days and the loop cut and slide deformation glitch really ruins it for me. note that i don't always have this problem but its a reocurring problem for me. Every time I try loop cut and slide this happens.
whenever i use the tool loop cut slide, blender automatically puts a huge dent in the cube.
You need to disable the X-Mirror option in the Tools panel > Options.