In some scenarios the toolbar appear to be displayed in two lines, when using custom tools in a toolgroup.

Possible resolutions:
1. Use only Icons to show the button;

2. Change the length of the text in the button, so that the tool group is rendered properly;

3.Change the width of the button. You could achieve that be creating a CSS rule like in this example:

.reToolbar .reTool_text[title="{Custom's button text}"]
{
      width:100px;
}