Periods being stripped from URL’s when saving

I have the same problem as described here:

https://www.ads-software.com/support/topic/periods-being-stripped-from-urls-when-saving/

“Permalinks are removing the period from the URL format pagename.htm. It displays correctly when editing the Permalink, but onced saved, it removes the period and changes the URL to pagenamehtm and this is causing significant problems”

My plugin version is 2.1.2.2 and the problem exists. Please help