The back button takes you back to the previous page only if the new page is opened in the same window or tab. I have just tested your page in an iPhone. As expected, it loads a new browser window.
When this happens on an iPhone, an icon at the bottom right of the screen displays a number showing how many windows you have open. Tap that number to reveal a slider showing all open browser windows, and swipe to return to the original page.
I don't have an Android phone to test it on, but I remember there's a similar way of moving between open windows/tabs.
Since both pages are on the ebblab.nl site, it seems pointless to use target="_blank".
Thank you David,
I changed it back since opening a new window is clearly not the solution for my problem.
When you open a page by clicking on the imagemap hotspot it opens nicely. But when you go back to the previous page with the iPhone back button and click again on a hotspot the phone loads the page but goes back to the previous page when it is loaded.
It happens only when you tap on the imagemap and instead of tapping on the imagemap of the page that opens you go back to the previous page using the back button on the phone, then tap again on the imagemap.
But if it is ilogical to do this I may have solved the problem because the imagemap is now on everey page and I am busy shortening the pages using collapseble div.
The problem exist but will not be noticed by most users