CALayer custom drawing glitch - ios

Question

I'm working on glow effect CALayer. I've created an UIView category. And my custom drawing gives me this strange animation:
Please, check my full code.
UPDATE:
I've added some code, that I think crucial.
- (void)setGlowHidden:(BOOL)glowHidden {
self.layer.masksToBounds = glowHidden;
self.clipsToBounds = glowHidden;
if (self.glowLayer == nil) {
self.glowLayer = [GlowLayer layer];
self.glowLayer.frame = self.layer.bounds;
self.glowLayer.parentView = self;
self.glowLayer.masksToBounds = NO;
self.glowLayer.contentsGravity = kCAGravityCenter;
[self.layer addSublayer:self.glowLayer];
}
//...
[self.glowLayer setNeedsDisplay];
[self.glowLayer performSelector:#selector(setNeedsDisplay) withObject:nil afterDelay:0.0];
}
//...
- (void)drawInContext:(CGContextRef)ctx {
CGFloat delta = MAX(self.glowSize, self.innerGlowSize);
CGRect drawingRect = CGRectMake(-delta, -delta, CGRectGetWidth(self.parentView.frame) + 2 * delta,
CGRectGetHeight(self.parentView.frame) + 2 * delta);
CGPoint offsetPoint = CGPointMake(-drawingRect.origin.x, -drawingRect.origin.y);
self.frame = drawingRect;
[self setNeedsLayout];
[self layoutIfNeeded];
UIGraphicsBeginImageContextWithOptions(drawingRect.size, NO, 0.0f);
// [self.parentView drawViewHierarchyInRect:rect afterScreenUpdates:YES];
[self.parentView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *textImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIGraphicsPushContext(ctx);
CGContextSaveGState(ctx);
if (_glowSize > 0) {
CGContextSetShadow(ctx, CGSizeZero, _glowSize);
CGContextSetShadowWithColor(ctx, CGSizeZero, _glowSize, _glowColor.CGColor);
}
[textImage drawAtPoint:offsetPoint];
CGContextRestoreGState(ctx);
//...
}