Hi!

In my org, I have the Opportunity object, that has a related list from a custom object named Proposta__c.
Proposta__c stores some Opportunity fields values, and a custom PDF as attachment, that contains other Opportunity informations.
Proposta__c records are generated only by a button, embedded in the Opportunity layout, as a Visualforce page commandButton (not a object's custom buttom).
So, in the Opportunity, the user clicks on this button, it calls a Apex extension class that I wrote, that creates a Proposta__c record with its fields, and generates/attach the PDF on this record.
Until here, everything is working as expected.

But, after create a Proposta__c record, I need open It, so I decided to use the onComplete commandButton property to do It.
The onComplete works fine to open the new Proposta__c record, but, when I use onComplete, the PDF attachment is generated as a blank page.
Even if I include the onComplete with no actions on it, the PDF still generate as a blank page.
If I remove only the onComplete property, the PDF is generated perfectly, with all its contents.

The point is: How can I generate correctly the regs and PDF, and then open it? maybe with a onComplete alternative..

Bellow are some tests fragments codes, to make it clearer:

proposta_pdf: The Apex extension class, that generates the Proposta__c record and its PDF attachment:

public class proposta_pdf{
    
    public     Opportunity     opp_temp, opp_reg;
    public     Id              prop_reg_id {get;set;}
    public     String          url_base {get;set;}
 
    // constructor ==============================
    public proposta_pdf(ApexPages.StandardController controller) {
        
        // Get base URL (+prefix, if community)
        this.url_base = URL.getSalesforceBaseUrl().toExternalForm() + Site.getPathPrefix();
        
        // Get other values
        this.opp_temp = (Opportunity)controller.getRecord();
        this.opp_reg = [
            SELECT     Id, Name, Amount, Prop_Versao__c
            FROM     Opportunity 
            WHERE     Id =: this.opp_temp.Id
        ];
    }
       
    // geenerate PDF bin ========================
    public Blob gera_prop_blob(){
        PageReference prop_pag = Page.Proposta_Mestre;
        prop_pag.getParameters().put('id',opp_reg.Id);
        
        Blob prop_blob;
        if(!Test.isRunningTest())
            prop_blob = prop_pag.getContentAsPDF();
        else
            prop_blob = Blob.valueOf('Este e um teste.');

        return prop_blob;
    }

    // create Proposta__c reg + PDF attachment ======
    public void salva_proposta_registro(){

        // validation
        if(this.opp_reg.Prop_Versao__c == NULL)
            this.opp_reg.Prop_Versao__c = 0;
        else
            this.opp_reg.Prop_Versao__c++;
        
        // create/save Proposta__c reg
        Proposta__c prop_reg = new Proposta__c(
            Oportunidade__c     = this.opp_reg.Id,
            Name                = this.opp_reg.Name + ' Ver:' + this.opp_reg.Prop_Versao__c,
            Versao__c             = this.opp_reg.Prop_Versao__c,
            Valor__c            = this.opp_reg.Amount
        );
        insert prop_reg;
                
        // update Proposta__c version stored in a Opportunity field
        update this.opp_reg;
                
        // create/save/attach PDF in Proposta__c reg
        Attachment prop_anex = new Attachment(
            ParentId             = prop_reg.Id,
            Body                 = gera_prop_blob(),
            Name                 = this.opp_reg.Name + ' Ver:' + this.opp_reg.Prop_Versao__c + '.pdf'
        );
        insert prop_anex;
        
        // retur ID to open new reg
        prop_reg_id = prop_reg.Id;
    }

}

Proposta_Mestre: The Visualforce page, rendered as PDF. The Proposta__c attachment:

<apex:page standardController="Opportunity" renderAs="pdf" applyHtmlTag="false" showHeader="false">
	
	Testing Opportunity My PDF
	<br/>ID: {!Opportunity.Id}
	<br/>Name: {!Opportunity.Name}
	<br/>
	<br/>End.
	
</apex:page>

proposta_botoes: The visualforce page that contains the button, embedded in Opportunity layout:

<apex:page standardController="Opportunity" extensions="proposta_pdf">
    <apex:form>
        <apex:inputHidden value="{!Opportunity.Id}"/>          
        <apex:commandButton 
            value="Save" 
            action="{!salva_proposta_registro}" 
            onComplete="window.top.location.replace('{!url_base}/{!prop_reg_id}');"
        />
    </apex:form>
</apex:page>

This is what the Opportunity detail page looks like:


And the Proposta__c record, created by the button:


When I do NOT use the onComplete in the button, the PDF is generated in the right way:


And finally, if I add the onComplete in the commandButton, only a blank page is generated:


Additionally, I already tried:
 - Add the extensions="proposta_pdf" in the Visualforce PDF page
 - Use the controller.addFields() method to pass the required fields
With no sucess.

I'm preety new in Apex development, so this can be just a detail that I didn't notice, or some mistake.. but after days searching a solution, I'm still not able to figure out how to fix it.

I'd apreciate some sugestions..
And sorry for my bad english, I'm still beginner :)
Thanks.