Setting 'skip page after print' to true does not force the second detail to the next page when using html format, and Report Composer does not execute a page break when print preview is used.
The problem is not the Report Composer but the way that Windows preview API handles the HTML page format. When Internet Explorer's print preview window pops up there are two drop down list boxes, one to select how many pages to display and the other to select the size of the document to display.
In the size list box the default value is "Shrink To Fit", that is the cause of the problem. When this option is selected it shrinks the HTML format to fit the page and it does ignores any next page characteristics. The problem can be solved very easily by making the browser fit the full screen using the restore up button in the upper right hand corner, and in the size list box select 100%. One that has been done the pages will show just one detail and then it can be printed with no problems.