Playback issue with ottavas

Trying to make life easier for a continuo player, I am transcribing a tenor-clef section of the basso continuo part into bass clef, but setting it an octave lower because it goes up to a high A-flat. Hence I will place an ottava line above those 9 measures.

The graphic part of this is not a problem, but during the orchestration process it's useful to hear a reasonably accurate playback of the score. Unfortunately, the score plays at the octave only for those notes under the original length of the ottava line as it was dragged from the palette (which extends from wherever it is anchored to the next barline). These lines can be stretched, of course, but any notes under the stretched part of a line (stretched with click-edit) play as written, not at the octave.

I have tried stretching the line both forwards and backwards; I get the same result in both cases. I also tried selecting the entire section to be covered by the ottava, and double-clicking on the palette--to see if I could create an original ottava line the length required--but that doesn't work (as it does for articulations and some other elements).

I have come up with a workaround, which involves setting separate ottava lines for each measure, then editing the properties to remove the end hooks and text and visually stretching the start of each new ottava back into the preceeding one. But it strikes me as odd that the system flag or whatever which signals 'play at the octave' is limited to the default length of the ottava. In the attached score, mm. 13-15 all play at the octave because I set individual ottavas for each (I left those in their original graphic form so you can see where they are); but in mm.16-20, only the first measure plays at the octave because that ottava line was stretched. The playback drops to written pitch on the first note of m.17.

Is there another (better) way to do this, or should this be considered a bug?

MuseScore 2.0.1, OS Windows 7 Professional.

Thanks.