Immediate mode with ImmediateModeShapeDrawer & high memory allocation?

I'm not entirely sure if this is a bug in how I use Shapes or a bug in Shapes itself, or if I'm just dumb and this is expected, but I'm drawing a few (~20) healthbars, each with its own `ImmediateModeShapeDrawer`, and getting around a 200ms GC pause around 2x per second. Looking at the profiler with call stack collection enabled at `GC.Alloc` points to shapes, and when I comment out my immediate mode drawing code all the GC pauses disappear.

Here's a few examples of the call stacks (not sure how to best report it, screenshots since Unity can't seem to copy from there)

The code itself is basically the `IMPanelSample` with some modifications, full code here https://gist.github.com/darthdeus/00374a19cda7c418400b94e414e213ff but it only draws rectangles and no text.