I'm reporting this for version 25 but I have experienced this issue since tiki was a teenager.
If you create a numbered heading with!!#Next Step Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
And later your either edit the whole wiki page with the drop down edit items from the top right of the wiki page or you do a section edit by clicking the little edit icon next to the header, it looses the # symbol every time and needs to be inserted again. Its quite annoying .
Don't use the wysiwyg wiki editor.
Edit wiki pages in text mode and then the hash symbols are not dropped.
To help developers solve the bug, we kindly request that you demonstrate your bug on a show2.tiki.org instance. To start, simply select a version and click on "Create show2.tiki.org instance". Once the instance is ready (in a minute or two), as indicated in the status window below, you can then access that instance, login (the initial admin username/password is "admin") and configure the Tiki to demonstrate your bug. Priority will be given to bugs that have been demonstrated on show2.tiki.org.
To help developers solve the bug, we kindly request that you demonstrate your bug on a show.tikiwiki.org instance. To start, simply select a version and click on "Create show.tikiwiki.org instance". Once the instance is ready (in a minute or two), as indicated in the status window below, you can then access that instance, login (the initial admin username/password is "admin") and configure the Tiki to demonstrate your bug. Priority will be given to bugs that have been demonstrated on show.tikiwiki.org.