Question: Optimization package in the Classic worksheet.

I was solving one Math puzzle and found out a strange behaviour of the Optimization package commands in the Classic Worksheet.

Let us minimize the function 7*x+3*y under the constraint 6*x+2*y >= 49 for non-negative integers. When I type

Optimization:-Minimize(7*x+3*y, {6*x+2*y >= 49}, assume = nonnegint);

in the Standard Worksheet (Maple 15), it works good and I get

which is correct. The help page ?Optimization/General/Options says that "The integer, nonnegint and binary values of the assume option are only accepted by the Optimization[LPSolve] command." So OK, I can also type:

Optimization:-LPSolve(7*x+3*y, {6*x+2*y >= 49}, assume = nonnegint);

and get the same result.

However, when I try to do it in the Classic Worksheet it doesn't work. When I try

Optimization:-Minimize(7*x+3*y, {6*x+2*y >= 49},assume=nonnegative);

then it is still OK. But when I type:

Optimization:-LPSolve(7*x+3*y, {6*x+2*y >= 49},assume=nonnegint);

I get Error, (in Optimization:-LPSolve) no feasible point found for LP subproblem

What more, when I type:

Optimization:-LPSolve(7*x+3*y, {6*x+2*y >= 49, x=8}, assume = nonnegint);

(I added x=8 constraint), the Classic Worksheet prints the message that "mserver stopped working" and I have to close the worksheet (I can not do anything else).

Does anyone know where the problem is?