On the Format Cells dialog, Alignment tab, the entry field for Text Orientation
in degrees does not allow you to delete the contents of the field. Presumably
this choice was motivated to avoid invalid entries, requiring an integer in the
range 0 to 359. However, it is unexpected behavior for a user interface and for
fast typists leads to unexpected results.

For example if the user has "63" in the field and wants to change it to "91",
the user might expect to be able to click on the field, placing the cursor at
the end of the field, then type backspace twice, then enter "9" then "1".

However, the second time they press backspace, the field will clear for an
instant, then it puts back the "6" the user just deleted, placing it after the
cursor.

Then, when the user enters "9" then "1", the field contains first "96", then for
a brief instant contains "916", which is replaced with "359".

As a keyboard-oriented user I find this field quite annoying. To me the sequence
of four key-presses in the example are one unified action, and I don't think
about them as separate actions. With this interface, I have to turn my attention
from what I was doing to understanding a quirky interface. I am classifying this
as an enhancement, because I assume the current behavior is what was intended,
but it's so distracting to me I'm tempted to call it a defect.

I think a preferable mode of operation would be to allow the user to make any
entries in the field they desire, but interpret any invalid entry as 0 degrees
rotation, for the "ABCD" example display, when the user clicks OK or navigates
out of the field. If there is an invalid entry when the user clicks either the
up or down buttons, the invalid entry should again be interpreted as 0, then
replaced by either 1 or 359 depending on the direction.