Angular checkbox gets updated even though ngModel doesn't - html

Question

I'm working on a shift arrangement app. In it I'm trying to create two tables that show which possible shifts each user has selected.
Both tables display the same data, but arrange it differently. Each table cell has a number of check-boxes that display the possible shifts for each person (in table 1) or the possible people for a shift (in table 2). A checkbox from table 1 that displays shift A option for person X will have the same data-bind as its equivalent checkbox in table 2, which displays person X option for shift A.
The purpose of this is to update the equivalent data in both tables simultaneously when the user couples a person with a shift. The problem: when a checkbox in table 1 is checked/unchecked, all of the check-boxes in table 2 gets checked/unchecked, as shown below:
Here is my template:
<div class="table-container" dir="ltr">
<h3>People</h3>
<table>
<thead>
<th>Name</th>
<th>Options</th>
</thead>
<tbody>
<tr *ngFor="let user of userPreferences">
<td>{{user.name}}</td>
<td>
<div *ngFor="let selection of userYesses[user.name]">
<mat-checkbox class="option-checkbox" dir="ltr" [(ngModel)]="selection.isSelected" name="usc">{{selection.option}}</mat-checkbox>
</div>
</td>
</tr>
</tbody>
</table>
</div>
<div class="table-container" dir="ltr">
<h3>Shifts</h3>
<table>
<thead>
<th>Time</th>
<th>Options</th>
</thead>
<tbody>
<tr *ngFor="let shift of totalShifts">
<td dir="ltr">{{shift.time}}</td>
<td>
<div *ngFor="let selection of shiftYesses[shift.time]">
<mat-checkbox class="option-checkbox" [(ngModel)]="selection.isSelected" name="syc">{{selection.name}}</mat-checkbox>
</div>
</td>
</tr>
</tbody>
</table>
</div>
And here is relevant component code:
this.userPreferences.forEach(u => {
this.userYesses[u.name] = [];
u.preferences.shifts.forEach(week => {
week.forEach(day => {
if (!day.shifts) return;
day.shifts.forEach(shift => {
if (!this.shiftYesses[`${day.date} ${shift.time}`]) this.shiftYesses[`${day.date} ${shift.time}`] = [];
if (shift.isSelected) {
let selection = new Selection(`${day.date} ${shift.time}`, u.name);
this.userYesses[u.name].push(selection);
this.shiftYesses[`${day.date} ${shift.time}`].push(selection);
}
});
});
});
});
The code seems alright to me, am I missing anything? Maybe it's a bug in Angular?
Thanks in advance!

Answer 1

In case anyone else experiences this issue -
After a few days of struggling with this, I stumbled upon this issue from Angular's git - https://github.com/angular/angular/issues/9230
I've read the following in kara's answer:
In the case that you don't want to register a form control, you currently have a few options:
1 - Use ngModel outside the context of a form tag. This will never throw.
<input [(ngModel)]="person.food">
After reading this, I switched the <form> tag into a <div> and everything works as expected now.