Paragraph will not inserted into list items.

src/model/utils/insertcontent.js

@@ -282,8 +282,8 @@ class Insertion {
 			return;
 		}
 
-		const mergeLeft = context.isFirst && ( node.previousSibling instanceof Element ) && this.canMergeWith.has( node.previousSibling );
-		const mergeRight = context.isLast && ( node.nextSibling instanceof Element ) && this.canMergeWith.has( node.nextSibling );
+		const mergeLeft = canMergeLeft.call( this );
+		const mergeRight = canMergeRight.call( this );
 		const mergePosLeft = LivePosition.createBefore( node );
 		const mergePosRight = LivePosition.createAfter( node );
 
@@ -327,6 +327,24 @@ class Insertion {
 
 		mergePosLeft.detach();
 		mergePosRight.detach();
+
+		function canMergeLeft() {
+			const previousSibling = node.previousSibling;
+
+			return context.isFirst &&
+				( previousSibling instanceof Element ) &&
+				this.canMergeWith.has( previousSibling ) &&
+				this.model.schema.checkMerge( previousSibling, node );
+		}
+
+		function canMergeRight() {
+			const nextSibling = node.nextSibling;
+
+			return context.isLast &&
+				( nextSibling instanceof Element ) &&
+				this.canMergeWith.has( nextSibling ) &&
+				this.model.schema.checkMerge( node, nextSibling );
+		}
 	}
 
 	/**

tests/model/utils/insertcontent.js

@@ -407,6 +407,25 @@ describe( 'DataController utils', () => {
 						'<paragraph>b</paragraph>'
 					);
 				} );
+
+				it( 'should not merge a paragraph wrapped in blockQuote with lists', () => {
+					model.schema.register( 'blockQuote', {
+						allowWhere: '$block',
+						allowContentOf: '$root',
+					} );
+
+					setData( model, '<listItem>fo[]o</listItem>' );
+
+					insertHelper( '<blockQuote><paragraph>xxx</paragraph></blockQuote><heading1>yyy</heading1>' );
+
+					expect( getData( model ) ).to.equal(
+						'<listItem>fo</listItem>' +
+						'<blockQuote>' +
+						'<paragraph>xxx</paragraph>' +
+						'</blockQuote>' +
+						'<heading1>yyy[]o</heading1>'
+					);
+				} );
 			} );
 
 			describe( 'mixed content to block', () => {