Playback from selection issue

I've just shifted across from version 3 to version 4 and am encountering a pervasive issue with playback from selection. According to the handbook, if you wish to playback all parts from a given bar, you select a single note in that bar and hit space or play. When I do this, about 80% of the time the playback restarts from bar 1. If I have selected an entire bar it will playback from bar 1 with only that part sounding, if a single note it will play the entire score but from bar 1. Other times, without any clear change in input on my end, it will playback from the selected note as expected. Is this is a bug? Or am I missing something.