Z probe repeatability - no data (3 replies)

I enabled z probe repeatability in the firmware, but when I run a M48 command, I get all 0s:

SENDING:M48 n10 V4
M48 Z-Probe Repeatability Test
Positioning the probe...
echo:busy: processing
echo:busy: processing
echo:busy: processing
Bed X: 100.000 Y: 100.000 Z: 0.000
echo:busy: processing
echo:busy: processing
1 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
2 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
echo:busy: processing
3 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
4 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
echo:busy: processing
5 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
6 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
echo:busy: processing
7 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
8 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
echo:busy: processing
9 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
echo:busy: processing
10 of 10: z: 0.000 mean: 0.0000 sigma: 0.000000 min: 0.000 max: 0.000 range: 0.000
echo:busy: processing
Finished!
Mean: 0.000000 Min: 0.000 Max: 0.000 Range: 0.000
Standard Deviation: 0.000000

When the test ends, the lcd screen shows an M105 command, and pronterface keeps echoing: echo:busy: paused for user

Am I missing something in the firmware? My probe works fine otherwise, z endstop logic is ok.