The wysiwyg editor 'sees' probably that it doesn't has any effect, thus it deletes it. Try to put a in it and see if it works. Otherwise, when your text is ready, copy all of the HTML and put it in a HTML block instead of a Content block. And make there your adjustments.

Thanks for reply.
I should explain it better...

I used fully described link with url and title...
I had the same issue is when i tried to put .js code - but issues with basic html elements it's slightly strange as i think

Like i said - code was valid - but all modifications were lost. And it works like that every time when i try to do similiar things.

using <a> tag on header elements should be possible - i don't see any issue related with it. Applying it from UI works fine - but i can't build some more sophisticated html structures.

Using HTML block is poor option due to my customer needs. They will not able to edit it in the future.

Any other thoughts?

Advanced mode...
But your question shown me some possible way to resolve that issue : custom mode with pugins control.. Thanks! :)

UPDATE:
Ok - i checked that - so - code validation could be turned off - but where are settings files?
Or how to set it in "custom mode" window?

Glad to help!