I do not believe this is an issue, at least I'm not getting those results when I conduct this scenario in a 2018 version.
I ran a scenario below and I do see for the same location code where I see a supply and a demand line where it adds inventory via a supply, and reduced inventory via a demand without the show include planning suggestions. This was two Transfers Orders, different days, with the opposite location codes in the header.
Running MRP/MPS, you shouldn't be getting suggestions both ways due to the sku cards only having one setting. But I believe the issue you may be having is perhaps you have cancel/new or change suggestions to existing transfer orders perhaps not showing up without the include planning suggestions…since you are running planning and haven't actioned the suggestions from planning.
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