APM Planner crashes when loading a secondary mission plan

Hi,

This problem pertains to re-uploading mission plans when controlling two aircrafts in APM Planner. More specifically, two 3DR Aero aircrafts with pixhawks running arduplane. The first aircraft is selected and a mission plan can be both loaded from a directory and uploaded to the aircraft. The second aircraft is then selected and a mission plan can be once again loaded and uploaded to the aircraft. The first aircraft is then selected once again and a new plan is to be loaded. However, upon loading a new mission plan itself, not uploading to the aircraft, APM Planner crashes. I was able to recreate the problem three separate occasions and it also persists even if I am controlling one aircraft in APM Planner. The error that is presented when the crash occurs is as follows:

Problem signature:
Problem Event Name: APPCRASH
Application Name: apmplanner2.exe
Application Version: 0.0.0.0
Application Timestamp: 55216195
Fault Module Name: apmplanner2.exe
Fault Module Version: 0.0.0.0
Fault Module Timestamp: 55216195
Exception Code: c0000005
Exception Offset: 0027298b
OS Version: 6.1.7601.2.1.0.256.1
Locale ID: 1033
Additional Information 1: 0a9e
Additional Information 2: 0a9e372d3b4ad19135b953a78882e789
Additional Information 3: 0a9e
Additional Information 4: 0a9e372d3b4ad19135b953a78882e789

Any assistance would be appreciated and more information can be provided on request.
Thank you!

Reproduce the crash in APM Planner using the reported sequence: load and upload plans for two aircraft, switch back, and load another plan, then retry with one aircraft. No source file or test is identified in the report; done means loading the subsequent mission plan no longer crashes and the reported access-violation scenario is covered by a regression check.

Written by the indexing model from the issue text.