MathType systems of equations

Question

Hi.
I'm having a problem with MathType's MathML processing engine. What i want is to set up a system of equations, and so i have MathML code like this:

<m:math display='block' xmlns='http://www.w3.org/1998/Math/MathML'&gt;
<m:semantics>
    <m:mrow>
        <m:mo>{</m:mo>
        <m:mtable columnalign="left">
            <m:mtr>
                <m:mtd>
                    <m:mi>x</m:mi>
                    <m:mo>&minus;</m:mo>
                    <m:mi>y</m:mi>
                    <m:mo>=</m:mo>
                    <m:mn>2</m:mn>
                </m:mtd>
            </m:mtr>
            <m:mtr>
                <m:mtd>
                    <m:mi>x</m:mi>
                    <m:mo>+</m:mo>
                    <m:mi>y</m:mi>
                    <m:mo>=</m:mo>
                    <m:mn>4</m:mn>
                </m:mtd>
            </m:mtr>
        </m:mtable>
    </m:mrow>
</m:semantics>
</m:math>

Then i try to insert this code into MathType window. Strangely i get just a bracket (i.e. with one-line height) instead of a real system sign. The MathML seems to be correct, moreover the one i obtained from MathType itself does the very same thing.
Is there a way to get over this bug? Maybe some weird property is needed to make it display properly?