Combobox not saving old choices

[Lisea123]

I have a form on my PowerApps. Data source is SharePoint. On this form I have 2 combo boxes that need multiselect. 
When the form is in New mode, the combo boxes work perfectly, list of items is from one SharePoint list and save to a text column separated by comma in another SharePoint list.  When it's in edit mode however, the Combo boxes show the original selected items as being selected but as soon as I make a change it will only save the added selected or if no change, the data is now blank with only commas. 

Formula on DefaultSelectedItems: 
RenameColumns(Filter(Split(txtgalReceivedFrom,","),!IsBlank(txtgalReceivedFrom)),"Result","Value")
Formula on Items: 
If(editMode = true, ColReceivedFrom.Result,varReceivedFrom)
Formula on OnSelect: 
ClearCollect(ColReceivedFrom,{Name:""});Collect(ColReceivedFrom,Distinct('ForwardTo-ReceivedFrom',ReceivedFrom))
Formula on OnChange: 
false
Formula on Update:
Concat(ddReceivedFrom.SelectedItems,Result,",")

What am I missing? 

[WarrenBelz · Accepted solution]

Hi @Lisea123 ,

Yes - one of the disadvantages of using that workaround (I have a blog on this) for a Combo Box that was really designed to refer to a table in the data source. If you want to change anything, you need to unselect everything and re-select it. Personally, I would go back to using a multi-select Choice column for your data and all will work as expected.

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[WarrenBelz]

Hi @Lisea123 ,

Just checking if you got the result you were looking for on this thread. Happy to help further if not.

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[Lisea123]

I changed them all to single select which works great. However, when the user edits the item and deselects the items from the combobox then click save (submit form), it keeps the last entry and won't allow for blank entry. Can you help with that? 

[WarrenBelz · Accepted solution]

Hi @Lisea123 ,

Set your Formula Leval Error Management in Advanced Settings to true

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[Lisea123]

Thank you for your quick response. I've set my formula level error management to true. I'm not certain what this will do as I'm not getting an error. I simply can't save the choice changes made in the combo box. 
example: on the form 2 different combo boxes will appear. If the used has originally selected the wrong box and entered an item, they will then go and edit the item. They would unselect the choice for the first combo box and select a choice from the second combo box. when they click save. The edited item is updated in SharePoint with the choice from the second combo box but the now blank first combo box is not saved. The item still shows the original selection and not the now blank choice. 

[Lisea123]

Never Mind.. I answered my own question above. 
(If this setting is off, PowerApps will check your data type before updating, blank is not choice type, so that's the reason why you not updated successfully.)
Thank you very much for all your help 🙂