[AvalonEdit] Underscores With Auto Completion

I've recently implemented the auto completion section of the AvalonEdit within my application, and found that typing underscores acts as selecting the current selection instead of continuing to filter the list.  

Example:

Start typing (everything is great):

Attempt to type an underscore (completes the line, and appends an underscore to the end):

All together with no underscores:

Is there any way to disable this functionality to allow underscores to filter the list as one would expect?  Any help is appreciated.