BP and SP will be restored to the values they had at the start of the instruction before the exception handler is entered. This is basically the case for all registers when any instruction causes an exception/fault.

OK. I've modified the CPU code to save SP for restoring it when an exception occurs, while BP is buffered instead of decreased(it's used only during execution, when processing the nesting level 1-X). So instead of decreasing BP(changing the register) and using it as a memory address to read, it now directly applies the address by taking BP-(nestinglevel<<1), leaving BP unaffected(since it's overwritten by the end of the function anyways, when succeeding and not used anywhere else further down the procedure).