Start with "870-801" (no quotes) in the RadTextBoxControl
Backspace to delete the '8' after the hyphen
With the caret index directly after the hyphen, enter a new character.
This will result in the newly added character being appended to the end of the text instead of at the caret index.
Please note: If the caret index is moved manually after deleting the "8", the new character will be inserted at the caret index as expected.
I have attached a sample project that replicates the issue. We are on the latest Telerik WinForms controls. (2021.2.511)