Hi Ben,
Thanks for your reply.
I activated the WordPress default theme and tested; the same problem still exists!
Conclusion:
As you mention, it’s a problem with the WordPress text editor!
I can’t tell whether there is a means for the period to be included, but If I type the point first, then the phrase, the point will appear at the end of the sentence even though I wrote it first!
For your help and patience, I will change my rating from 4 to 5 stars.
Thanks!