Issues with partial geospatial index

I’m having weird errors with mongodb’s $near when using an index that includes a partialFilterExpression,

Steps to reproduce

use testDB;
db.locations.insertOne({gps: { type:"Point",coordinates:[-122.44629668762029, 37.67360721311997]}})
db.locations.insertOne({})
db.locations.createIndex({gps:"2dsphere"}, {partialFilterExpression:{gps:{$exists:true}}})
db.locations.find({ gps: { $near: { $geometry: { type: "Point", coordinates: [-122.46316650979725, 37.664362562900465] }, $maxDistance: 2000 }})

Error:

error processing query: ns=testDB.locationsTree: GEONEAR  field=gps maxdist=2000 isNearSphere=0
Sort: {}
Proj: {}

Expected output: the query returns the single valid document

System information:
MongoDB Version: v7.0.1
Distro: ArchLinux
Kernel version: 6.6.4-arch1-1

Looks like using a sparse index fixed the issue, however this might be still something to look at.