How to make sure newly created connectors are straight?

It looks like this has been a common question for ages ;). You can change default connector style by editing "Dynamic Connector" master in the document stencil (in your case, set it to be "straight").

To do this:

  1. Open the "Shapes" sidebar
  2. Hit the flyout icon next to "More Shapes" and select "Show Document Stencil"
  3. At the bottom a new panel shows which contains "Dynamic connector": right click it, and under "Edit Master" select "Edit Master Shape"
  4. Select the connector on your screen (should be a line with one right angle)
  5. Use the ribbon (Design > Layout > Connectors) to set it to "Straight"
  6. Close the window top left with the [X], and choose "Update the connector and all of its instances"

New connectors will now default be routed as straight connectors.

Here are some other sources that tell a similar story:

  • Answers.Microsoft.com
  • Visguy.com