The "Sell" dialog has been changed to not accept an empty string for "Sell amount" and "Sell price". Let's say the current value is "MP". It's fine to delete "P", but if you also delete "M", the price is an empty string. In previous versions, the game shows you an error dialog when you press "Confirm". Now, it does not allow an empty string.

Tips:

• If you have to delete the string up to the first character, it's very likely that you are making a mistake. MAX and MP are fine choices as default values for "amount" and "price". Even when you need to use different values, it's usually something based on MAX and MP (MP*0.9, MP*2, etc.).
• You should read the in-game documentation of Corporation (it's also available at https://github.com/bitburner-official/bitburner-src/blob/stable/src/Documentation/doc/advanced/corporations.md). You have made many classic mistakes in your Corporation.

Although I agree with what you said, this is rather awkward behavior for a text box. "M" is just as invalid as "", so why is "M" allowed but "" is not? It feels like the behavior of deferring the error until later was more correct.