| Common. Normal for this time of year..:-) Sure you can keep it growing....Alot slower than in full sun, on sunny hot summer days.. It will constantly push out new growth from the top, unless you withdraw light all together.
In fact if you used no lights at all, and just stuck them in a window, dependent on the winters light only, they would still grow a tad bit. The thing is, you will never get them to be fully leafed out, unless you provide 14 hours or more of full strength hot light and very warm conditions.. perfect conditions..
Hard to mimick in winter, especially in Canada.
By nature they want to drop leaves at this time of year, especially in the fashion as you describe. Why even in Texas they are dropping leaves as you described..
My local nursery owner has a few, loosing leaves like crazy, like yours, in full sun, and in a hot greenhouse anyway..Don't fret.:-) Not to worry. They will not die, nor will they stop "growing" if you providing them some light.
They will almost stop pushing leaves, and maybe not at all, if you withdraw all light and warmth. Your major concern should be your "watering" habits, and "root rot". Be careful, especially if your soil is not porous and free draining...
At this time of year, your soil should not be wet more than a couple days at a time if in dormancy stage..
If so, you will loose them unless you are keeping them in active growth under warm lights and a warm enviroment..;-) Dormancy does not mean it is entirely asleep as some of our outdoor plants, such as perenials, it just means it is growing at a much SLOWER pace..Believe or not, they will still look for a drink, even in dormancy stage.. Just keep it alive, and the full strentgh of spring sun will bring it back to full leaves, and possibly flowers too..;-) Sorry about spelling. Time fleeted me and I had to leave fast..Hope this helped.;-) | 
