"Unknown Invocation" in timeline when using CL-Server mode

[gix]

Tracing a build with CL-Server mode enabled:

    <UseMultiToolTask>true</UseMultiToolTask>
    <EnforceProcessCountAcrossBuilds>true</EnforceProcessCountAcrossBuilds>
    <EnableCLServerMode>true</EnableCLServerMode>
    <BuildPassReferences>true</BuildPassReferences>
    <AllowParallelCompileInReferencedProjects>true</AllowParallelCompileInReferencedProjects>

results in many unknown invocations:

Each blue bar in the timeline is unknown. Curiously some invocations are displayed properly (other colors). Setting EnableCLServerMode to false works fine. Not sure if this is an issue with how vcperf analyzes the trace or how the compiler emits events.