Hand signaling while decelerating I'm nervous about hand signalling (taking a hand off the handle bar) while I'm decelerating: I'm worried that my body being pushed forward will act on the one remaining hand and change the angle of the front wheel.

So I'm sometimes not signalling as much as I'd like to (e.g. while I'm decelerating): as much as I would in a car.

Is this a known problem? Is there a work-around or solution?

This is for riding in city traffic. For example on a main road, relatively fast with cars following, I want to slow down before turning off onto a side street.
Yes, it's a known problem, at least to me. The work-around is not to signal, or to use head-turning and lane positioning as a signal.

What I do is very dependent on the situation. In the worst case, fast moving traffic on a busy, multilane road with no bike lane/bus lane/parking that would allow me to slow down out of traffic I will overshoot and just pull in at the next opportunity. If I knew about it in advance I'd avoid that road. My experience of signalling and slowing down, forcing the moronist behind me to also slow, is that it doesn't help. I get signals back, shall we say.

Cyclists in Melbourne do signal more than they do in Sydney, but rarely to motorists. The most common is the right arm out "I'm pulling out in front of you" which when done assertively works almost all the time for persuading motorists to let you turn. (left arm/move left for countries that ride on the right hand side of the road). The slowing down signal I don't recall ever seeing except in primary school. 

Signals between cyclists are much more common, but that's because they're safer, easier and the following cyclist is more likely to notice them.