I think that's what Simon means by having to do three strokes PHROLG stroke PHROLG to interpret a single Plover stroke from within normal typing. It would nice if including another key in the stroke (e.g. space) would interpret the rest of the chord as Plover and immediately return to normal use.
There is a long discussion of the pros and cons of using the space bar as a function key here:
Rethinking: Caps Lock+stroke might be better, making it less likely for a fast typist to produce a spurious stroke