Wasn't sure which subforum to post this in as my problem involves issues with both the editor and Unity.

I'm using IK constraints to keep a character's hands attached to a gun bone. This works as expected initially.
Loading Image

Skeleton hierarchy:
Loading Image

In order for the player to be able to control the aim of the gun dynamically I added another IK constraint affecting the gun bone. When this constraint is applied the gun bone rotates as normal and the IK constraint attachments for the arms also move correctly. However only one of the arms follows its constraint with the other ignoring it. (The head also has an IK constraint attached to the gun bone which continues to work correctly.
Loading Image

I tried recreating the approximate shape of the relevant parts of the skeleton in a new file and encountered the exact same problem. I then tried it again but parented the gun bone to the IK attachments in a different order and this time neither of the arms would follow their constraints.

After this I tried exporting the skeleton to Unity and oddly the problem was not present. Both arms remain attached to the gun when the gun's IK constraint is moved.
Loading Image

However I then encountered an additional problem when flipping the skeleton (through the Skeleton Utility flipX parameter). The gun constraint appears to be positioned correctly but the gun bone faces 180 degrees away from it (with the arms still attached as they should be).
Loading Image

I don't know if these issues are related at all considering that they both affect the same bone but are different in nature. Any suggestions of what the issue might be or possible workarounds would be greatly appreciated.