So this is what my line meter looks like. It uses a Transformation Matrix to "spread out" the lines so that the behaviour is more visible:
It 'was' a single defined line, now it is showing the added width the Transformation Matrix adds. The code is the same before and after the Alpha was installed.
For some reason (probably something internal to GDI+), your example of TransformationMatrix and others I tried when debugging this issue caused GDI+ to render the line's width at the defined LineWidth, instead of the "transformed" width (applied by TransformationMatrix). Using a more basic example, like the one provided in the link above, TransformationMatrix was clearly being applied correctly. Since, in most cases, TransformationMatrix can modify what a meter does draw, we decided to revert the changes that forces the line to be drawn at the defined LineWidth.
The Good:
As described here, since GDI+ is giving us inconsistent behavior, we have decided to make a new option called "TransformStroke" that will control this behavior.
This means you may have to add this option to the Line meter(s) of older skins if they are affected from this issue. Simply add the following option to the meter: TransformStroke=Fixed