Auto-selection of numerical data doesn't work

[alexsb]

In this example:

The numerical data is given as error. Maybe that's because of the first row, but that shouldn't matter for two reasons:

• in a largely numerical column, a string should be identified as an error / NaN
• This shouldn't be considered as data in the first place (see #48)

Even after I set the first row, to an identifier, it still shows "error" - I guess it doesn't re-evaluate?