Inaccurate value for the line width in Change Style dialog

The error occurs in Change Style dialog at the Line width combo. The selected value often becomes -1.

For example, if I select 5 in the width combo, then click apply, the line changes OK.
But then if I click to configure something else, the width line combo value becomes -1.

I figured there's something wrong with SLDs.width(Stroke) method in UDIG, as it always returns -1 and the Stroke parameter is OK.