set() on onSelect() action causes ember-table rows to be cleared.

Hey Chris, I have a question. I have a basic ember-table execution that loads data as intended, but when I do an onSelect action, it clears out my rows. Is there something that my onSelect is doing incorrectly?
Basically this is my ember-table body:
{{#table.body
rows=workingModel
rowSelectionMode='single'
checkboxSelectionMode='none'
selection=selectedRow
onSelect=(action 'selectRow')
as |table-body index|}}
{{table-body.row class="table-body-row" }}
{{/table.body}}

And this is what the action selectRow does:
selectRow: function(selection) {
let previousPartName=this.get('selectedPartName');
this.set('selectedRow',selection);
this.set('selectedPartName', selection);
},

Start with the provided table.body usage and the selectRow action, then reproduce the issue with rows=workingModel and the shown selection settings. Trace why setting selectedRow or selectedPartName causes the rows to clear; done means selecting a row leaves the table rows intact.