Had an interesting anomaly this morning in Calc, version 5.x using Ubuntu 16.04.
In a 'general' formatted field (default), I entered "April" without the quotes.
By mistake, I hit the CAPS key. About 10 lines down, entered "aP", starting to type April with the caps on.
Calc saw the April above so it displayed April. . . .with the red underline indicating I spelled it wrong, yet it
displayed identically to the above April.
Two issues:
1) It looks like the aPRIL is saved in the cell because that is what was actually entered, but April is displayed.
2) The spell check is performed against what is stored in the cell (seems reasonable), not what is displayed.
John