[Bug] Arithmetic instructions cause two pre-decrements/post-increments

[PietHelzel]

Current behavior and impact: When running an arithmetic instruction with an addressing mode of post-increment or pre-decrement, the affected instructions are incremented/decremented twice.

Steps to reproduce:

1. Execute an arithmetic instruction with a field containing a pre-decrement or post-increment address mode.
2. Observe the changes in the instructions being addressed.

Expected behavior: The increments/decrements are only done once.

Acceptance Criteria:

• [ ] The increments/decrements are only done once