al3xicon: We've actually ran into some similar issues the past couple of years, primarily seen on negative BIN inventory, while on hand was 0. But the fix is useful anytime BIN quantities do not match On Hand: Step 1: Adjust quantity necessary to make BIN equal to Zero. You will adjust this from the BIN being affected. This will send you in the opposite direction for On Hand (i.e. if you showed zero OH, now you'll show a negative or positive).
Step 2: Access item record and remove any preferred bins from the item/location in question.
Step 3: Go in now and make the opposite adjustment of what you've just made (getting On Hand back to correct quantity), but DO NOT select any BIN. Since none is preferred system will not allocate to a BIN, and now both On Hand and BIN quantities will be correct.