I upgraded an site from 1.5. (jUpgrade) to 1.7.2 to 1.7.3 all worked, no errors, no tags got stripped. In backend as Super Admin.
Today I upgraded from 1.7.3 to 2.5.0 and ALL html tags and any formatting got stripped on each article I edited. Disabling TinyMCE did NOT solve the issue, the tags got stripped out and all formatting was lost.

Solution: The solution was to disable the textfilter in the configuration - the setting was "standard blacklist". I set that to "no filtering" and it worked again. Now i switched back to "standard blacklist" and it is WORKING???
Any idea why this happens? On two other sites where I moved from 1.7.3 to 2.5.0 this did not happen.
greets