In edit, periods are not accepted

Atlassian Confluence 5.3.4 for CA Wiki pages.

We use Wiki for our knowledge transfer in my group. I have found an annoying problem when editing a Wiki page - it seems to ignore the period. That is, if I am editing a Wiki page, hit the end of a sentence and type a period '.' - it does not show up (and cursor does not progress one space).

If I notice it, I can type a few spaces with the space bar, then back up using the arrow keys (NOT the backspace), so the blanks are still there, and then type the period with no problem. Once I have done that, the periods work correctly from that point on, unless I get ahead of the entered blanks or not.

Thanks