QGIS » QGIS Application

I recently upgraded to QGIS 2.12 from 2.10 on Ubuntu 15.04 and one of my projects lost the data dependent overrides on the linewidth and colour of a line pattern fill of a vector layer.

I have a digital elevation model which I segmented and processed to a vector polygon layer, and used the average slope, slope direction, and curvature from the attribute table to style a line pattern fill, and an SVG marker line pattern fill.
This drew arrows in the downslope direction, which were thicker for steeper slopes, and coloured according to the longitudinal curvature. An example can be seen at my blog: [[http://skrifennow.blogspot.co.uk/2015/10/a-greyscale-version-of-my-maps-in.html]]

I use the following expressions:
for colour: case when RAT_LngtCrv_Mean > 0 then color_rgb(min(255,255*5*RAT_LngtCrv_Mean),0,0) else color_rgb(0,0,min(255,-255*5*RAT_LngtCrv_Mean)) end

for linewidth (using map units - metres): case when RAT_Slope_deg_Mean > 2.25 then max(20*((RAT_Slope_deg_Mean - 2.25)/ 90),0.4) else 0.0001 end

for size of the SVG arrow: case when "RAT_Slope_deg_Mean" > 2.25 then max(75*sqrt((RAT_Slope_deg_Mean - 2.25)/ 90),5) else 0.0001 end

for angle (working): 90 - RAT_Aspect_deg_mean

However after upgrading to QGIS 2.10, the data dependent styling of the line fill has disappeared as seen in the attached file. There is only the default black colour and linewidth, although the slope direction still works.

I am wondering if this is a bug?