The Alert component sizes itself based on content and doesn’t respond to setSize calls. However, the sizing doesn’t take embedded fonts into account and cuts off text when using embedded fonts.
To fix this bug we need to add two lines, one to mx.controls.alertClasses.AlertForm and another to mx.core.ext.UIObjectExtensions.
First in mx.controls.alertClasses.AlertForm find the getSize() function and add this line right before all of the current textMeasure_mc references.
textMeasure_mc.embedFonts = tf["embedFonts"];
Then in mx.core.ext.UIObjectExtensions find the TextFormat.prototype.getTextExtent2 mixin and add this line right after (and outside) the if statement.
_root._getTextExtent.embedFonts = this["embedFonts"];
If this bug is affecting you, you can choose to either make these changes directly to the core classes or create a local copy of the classes and change those, with a reference to them in each FLA’s classpath.