are canvas coordinates limited to 32k

I've been experimenting with placing widgets inside a canvas. When I tried to test it's performance on lots of widgets (in a column) I am seeing the last few widgets not being displayed when the code does
[winfo reqheight $content]
where content is a frame and the value returned is over 32768 (actually starts failing just shy of that value).
This naturally leads me to suspect there's a 16 bit issue here.
I'm testing on windows 10, with 8.6 and 9.0 and get the same results.