IE11 clears password fields on page refresh: - postback

Question

Happens only in IE (Chrome and Firefox, no issues... go figure)
I have a page where customer's can update their details (name, address,password etc.) and everything is working fine, however if the customer submits the form (which also works fine) and then presses the back button all the customer's information will repopulate the form except for the password field.
My boss would like this to repopulate as well, like it does in Chrome and Firefox, but IE won't do it. I'm hoping it's something simple I've missed but I can't see it. I've tried adjusting the lines where the text fields are populated to match the rest of the form, but that just results in empty fields. Code below.
Page_Load
If TypeOf Session("Customer") Is GPCUser Then
c = CType(Session("Customer"), GPCUser)
Else
Response.Redirect("default.aspx")
End If
If Not Page.IsPostBack Then
If c.CustomerID > 0 Then
'populate the table
lblAccountName.Text = c.AccountName
txtFirstName.Text = c.FirstName
txtLastName.Text = c.LastName
txtEmail.Text = c.Email
txtAddress.Text = c.Address
txtSuburb.Text = c.Suburb
txtCityTown.Text = c.City
txtPostcode.Text = c.PostCode
txtPhone.Text = c.Phone
txtMobile.Text = c.Mobile
'chkNewsletter.checked = c.Newsletter
txtPassword.Attributes.Add("value", c.GeneratedPassword)
txtConfirmPassword.Attributes.Add("value", c.GeneratedPassword)
'txtPassword.Text = c.GeneratedPassword
'txtConfirmPassword.Text = c.GeneratedPassword
Dim subscriptions As ContactSubscriptions = New ContactSubscriptions(c.CustomerID)
chkGenernalNewsletters.Checked = subscriptions.IsGenernalNewsletters
End If
Else
End If
Update Button
If TypeOf Session("Customer") Is GPCUser Then
c = CType(Session("Customer"), GPCUser)
Else
Exit Sub
End If
c.AccountName = lblAccountName.Text
c.FirstName = txtFirstName.Text
c.LastName = txtLastName.Text
c.Email = txtEmail.Text
c.Address = txtAddress.Text
c.Suburb = txtSuburb.Text
c.City = txtCityTown.Text
c.PostCode = txtPostcode.Text
c.Phone = txtPhone.Text
c.Mobile = txtMobile.Text
'c.Newsletter = chkNewsletter.Checked
c.GeneratedPassword = txtPassword.Text
c.CustomerUpdatedRequired = false
'Update password field
txtPassword.Attributes.Add("value", c.GeneratedPassword)
txtConfirmPassword.Attributes.Add("value", c.GeneratedPassword)
GPCUser.AddUpdateCustomer(c)
subscriptions.IsGenernalNewsletters = chkGenernalNewsletters.Checked
subscriptions.Save()
Session("Customer") = c
lblMessage.Text = "Your details have been successfully updated."
pnlUpdateAccount.Visible = False