I submitted a complex compile problem last night and tonight I distilled it down to a single very strange problem. 

In the file ClassA.h, uncomment line 83 (see comment) and the compile fails with 2 errors and 25 warnings. Comment out that line and it compiles and executes just fine. 

Note that the array in question is sized for 18 integers, but it only allows 16 to be defined.

Yes. I get the same results in the Arduino IDE. It appears to be some issue with the compiler and I notice that the "commands[18]" array only allows 16 members. It is the 17th member that causes the failure and the failure is almost catastrophic. The two error messages ("10:7 error: this is the insn" and "10:7: error: unable to find a register to spill in class "POINTER_REGS") are quite arcane and don't tell me anything about my code. They suggest some sort of failure in the compiler itself. And the warning messages (all 25 of them) do not give me any useful information about my code.