Point Instanser incorrect processing

[iqch]

Description of Issue

usdview or its stageView widget shows incorrectly point instancer content in frames without instances defined - just keep content of latest non-empty state

Steps to Reproduce

#usda 1.0
(
endTimeCode = 3
startTimeCode = 1
)

def PointInstancer "Proximities"
{
rel prototypes =
quath[] orientations = []
point3f[] positions = []
point3f[] positions.timeSamples = {
1: [],
2: [(3, 0, 0),(6, 0, 0)],
3: [(3, 0, 0),(6, 0, 0),(9, 0, 0)]
}
int[] protoIndices = []
int[] protoIndices.timeSamples = {
1: [],
2: [0,0],
3: [0,0,0]
}
float3[] scales = []
float3[] scales.timeSamples = {
1: [],
2: [(1, 1, 1),(1, 1, 1)],
3: [(1, 1, 1),(1, 1, 1),(1, 1, 1)]
}
}

def Sphere "ball"
{
color3f[] primvars:displayColor = [(1, 1, 1)]
double radius = 1
token visibility = "hidden"
}

screengrab
https://vimeo.com/424909279

System Information (OS, Hardware)

USD20.05 Win10 MSVS2017 Win64
Python3.6

Package Versions

Build Flags

[jtran56]

Filed as internal issue #USD-6100.