Ionic-scroll scrolls when under an ion-select (ios only)

I have an application where I use an ion-scroll to scroll the main contents rather than having the ion-contents scroll. I do this as I want a fixed filter at the top of the page.

I have markup like below…

    .mm-card-page-content {
       height: 100%; 
        display: flex;
        flex-direction: column;
       background-color:white;
    }

   .mm-card-inner-scroll {
      flex-grow: 2    
      } 

	<ion-content scroll='false' no-bounce>   
		
	  <div class='mm-card-page-content'>

	  <ion-grid >
		<ion-row class='mm-search-row'>
		  <ion-col class='mm-card-searchbar-col'>
			<ion-searchbar placeholder="{{'LABEL_SEARCH' | translate}}"
			   class='mm-card-search-bar' [(ngModel)]="searchText" (ionInput)="filterItems($event)"></ion-searchbar>           
		   </ion-col>
		  <ion-col class='mm-filter-col'>
			<ion-option ion-button (click)='filterClick()'>
			  <ion-icon md='ios-funnel' name='funnel'></ion-icon>
			</ion-option>
		  </ion-col>
		</ion-row>				
	  </ion-grid>
	   
	   <ion-scroll class='mm-card-inner-scroll' scrollX="false" scrollY="true">    
		  <div *ngFor="let item of filteredData" class='mm-card-outter' >      				
			   <!--  contents  -->				
		  </div>
	  </ion-scroll>

	  </div> 
	</ion-content>

To stop the main content scroll I have the ion-content scroll='false' no-bounce, and I have the ion-scroll with scrollY="true" to scroll the main contents.

I use the filter button to show an alert…

let alert = this.alertCtrl.create({enableBackdropDismiss: false});
.. add options...
alert.present();

This work fine in the browser and on Android, but on ios, I can scroll the contents of the ion-scroll. Also if the alert does not have scrollable contents, then if I try to scroll (swipe my finger up and down) on the alert, then the ion-scroll under it does the scrolling.

My only work around at the moment is to set a variable when the alert if presented and bind to the scrollY ie

<ion-scroll  [scrollY]="!filterOpen"

but you can see the ion-content jump slightly when you do this.

Has anyone else had this problem, and know of any fix?

Thanks in advance for any help!