How can I simply create a text frame with perfect rounded ends?

Question

I'm recreating a new edition of a book that was originally created in Quark. It uses round-ended text frames. When using the simplest method of corner options, the ends aren't proper semicircles, even though the radius is set to half the height of the frame.
The other problem is that I can't reduce the width sufficiently to make it look balanced. I use the direct selection tool to close in the right-hand end, so that I don't distort the shape. There's no right indent for the paragraph, but as I reduce the width the text breaks into two lines, even though I've greater space after the text than the left indent. My best solution was to create the shape in Illustrator and copy and paste into InDesign, assign text content, centre thte text vertically, use 3mm left indent. I still couldn't pull the right-hand end in tight enough. So I had to resort to making a group of the lozenge shape with a normal rectangular text frame on top.
Does anyone know why these problems occur, and can Adobe improve the corner option?

Answer 1

One last refinement: It's convenient if the script allows you to Undo/Redo its actions -- let me add that for completeness' sake. The following is the complete script again, no further editing required.
//DESCRIPTION:Overlay round corners on a single textframe
// A Jongware Script 2-Apr-2012
app.doScript(function(textframe){
if (textframe instanceof Group && textframe.pageItems.length == 2)
roundedRect = app.selection[0].polygons[0];
textframe = app.selection[0].textFrames[0];
textframe.properties = {strokeWeight:roundedRect.strokeWeight,strokeTint:roundedRect.strokeTint,strokeColor:roundedRect.strokeColor};
roundedRect.remove();
app.selection[0].ungroup();
left = textframe.geometricBounds[1];
right = textframe.geometricBounds[3];
height = textframe.geometricBounds[2] - textframe.geometricBounds[0];
center = (textframe.geometricBounds[2] + textframe.geometricBounds[0])/2;
radius = height/2;
leftRounded = textframe.parent.ovals.add({geometricBounds:[center-radius,left-radius,center+radius,left+radius]});
riteRounded = textframe.parent.ovals.add({geometricBounds:[center-radius,right-radius,center+radius,right+radius]});
rectBetween = textframe.parent.rectangles.add({geometricBounds:[center-radius,left,center+radius,right]});
roundedRect = rectBetween.addPath([leftRounded,riteRounded]);
roundedRect.properties = {strokeWeight:textframe.strokeWeight,strokeTint:textframe.strokeTint,strokeColor:textframe.strokeColor};
textframe.properties = {strokeWeight:0};
app.select(textframe.parent.groups.add([roundedRect,textframe]));
}, ScriptLanguage.JAVASCRIPT, app.selection[0], UndoModes.ENTIRE_SCRIPT, "Overlay Round Corners");