When you prompt a user for consent (using the common tenant) with the Microsoft identity platform endpoint, the user sign in experience will vary depending on the underlying identity behind their credentials.
A person who only has an MSA identity will be directed to the MSA sign in page.
A person who only has an Azure AD identity will be directed to their organizational sign in page.
A person whose credentials are valid in both the MSA and the Azure AD domains will encounter a disambiguation page that asks them to choose between their personal and their work or school identity. This disambiguation will always be present so long as this user has two identities tied to the same email address. The user can stop seeing this by changing the email address of their personal Microsoft account. For more information see https://cloudblogs.microsoft.com/enterprisemobility/2016/09/15/cleaning-up-the-azure-ad-and-microsoft-account-overlap/.
Note
You should handle operation error codes 122 through 125 to help users of your application select the correct credentials i.e., work versus personal account.