HP Prime "Cannot Find Solution" when solving two equations

[dae]

I put these 4 equations into Solver, and it reported "Cannot find solution"

A-B=7
2*B+3*B-3*C+B-A=0
X*C+2*C-7+3*(C-B)=0
B=2.273

I replaced the 3rd equation (starting X*C) with one isolating X to the left
of the equal sign, and it solved the equations.

I went back to the original 3rd equation, removing the changed
equation, and this time it solved.
Why would it not solve one time, but solve another time?

I had the same results using the physical Prime G2 and the virtual unit.