Rotating bones - cummulative error in angles

I’ve just been playing with the new offset bone thing, but along the way I noticed that when you have a lot of repeats of an action in the NLA, where bones are rotating, they get more and more inacurate.

Here’s an example blend file:

It’s just a single bone which rotates by 90 degrees every 2 frames.
The action is for one complete cycle, and is repeated 10 times.

If you look at where the angle should be -90 degrees, on frames 3, 11, 19, etc, it seems to get about 0.4 degrees off each time it goes around. By frame 75, the angle is -86.208, which is quite a noticeable error.

I tried all my old blender versions and it was the same, except for 2.37a. This needed the strip converting to an NLA strip to get it to go around more than once, but after that it looks perfect for each cycle. Although it shows quaternions in the display rather than degrees.

Is this worth reporting as a bug? Or do you reckon it’s a feature?