Completion when cursor is before word

We are using the SyntaxEditor with auto completion for our very own language.

We see the following development: When we type an expression, everything is ok.

But when we try to outline the expression with spaces in the editor, the completion provider seems to look at the following character, founds the whole word in its list, and submits it, making the cursor jump after the word.

Is is possible, that when we only enter a space before a word that is already fully submitted, the completion provider can ignore it, and not submit the only entry it finds, because its already there?

Example:

TRUE OR FALSE is a valid expression in our language. When typing TRUE [space] the list comes back with several suggestions including OR, so we select OR, type [space] and enter FALSE into the syntaxeditor.

Now when we set our caret before OR, like so:

TRUE[space][caret]OR[space]FALSE

and type a [space], the completion box comes up with only OR, in stead of the complete suggestions list. A second [space] submits this OR and jumps the caret over it, placing the space after OR resulting in:

TRUE[space]OR[space][caret][space]FALSE

instead of the expected:

TRUE[space][space][caret]OR[space]FALSE

How can we resolve this problem?

Thanks