If the timing side bush was not line bored accurately then the crank will not travel through the bush as far as it should but will feel as if it has ( will go through as far as the slight taper of inaccuracy will allow) so shimming the other side will give you the clearance required, then as the timing bush beds in the crank will travel through a bit further and your end float will increase.
I'm speaking from experience as this happened to me, although I never got as far as the engine running due to it being so far offline the crank actually nipped up when tightening the cases fully, the line boring inaccuracies could be very small but enough, took it back to the shop with a new bush and they got it second time, they could offer no reason for the first one being off but agreed that was the problem