DVX Standard regularly puts certain proper nouns (countries and so on) in individual segments for some reason.
You are probably talking about Word documents. Word likes to put certain nouns (e.g. place or company names) between invisible tags which throw DVX off track. To get rid of them, go to Tools/Options/Save and deselect "Embed smart tags" and "Embed linguistic data" and then resave the document.
When I come to export my document, I systematically click "yes" in that apparently pointless "there are missing spaces..." box. In some projects this doesn't seem to fix spaces for these specific orphan segments: the word is stuck to the next one and I have to go through and fix this manually in the exported document.
Try running the "Accept all multiple matches" command from the right-click menu before export (although failure to do so usually results in double spaces rather than missing ones). After that, use the option for checking space mismatches in the QA menu (not sure if this is available in the standard version). I have never had a problem with missing spaces after using this option from the QA menu.
Like you, I have also experienced unreliability when using the automatic correction of missing spaces upon export. Therefore, when I get the message about missing spaces, I always click "No" and redo the QA check before exporting the document again.