Why do the statements eval(sign(x),x=-2) and subs(x=-2,sign(x)) both give plus one while sign(-2) gives -1 as expected?

I want to graph the portion of the plane 2x + 3y + z = 6 that are located in the first octant of a xyz coordinate system. The following implicitplot3d should in principle do it:

The fsolve in the attached code took 45.615 sec to execute. For Delta >= 0.15 the execution time was only about 0.5 sec. For Delta = 0.12 and Delta = 0.11 the execution times were about 400 and 600 sec, respectively. Why does the execution time increase with orders of magnitude when I decrease Delta? And how can I speed up the process? Henning

Can anybody explain why the same dsolve-command gives the correct results in Maple 13 and an unexpected complex result in Maple 15?:

Please, consider this example:

I wonder why the match function returns TRUE and expressions that depend on the main variable x. I hope that someone can give me an explanation.

Best, Henning