I'd have to think its most likely gradients in the processing as Marco's deep image does not show anything and its a very deep version of this object.
//www.glitteringlights.com/Images/Nebulae/i-BrmvbBj/A
Its easy to have happen when there are gradients.
Send me a PM and I'll show you a way to get rid of the gradients that will take care of that.
Greg.
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