Could be that tabular figures are default...see if there's a proportional one somewhere in the glyph palette?

For tabular figures, this is indeed designed deliberately. It's this, or an extremely thick '1'!

(It's even more visible in the otherwise very agreeable Gill Sans.)

Some sans typefaces have a large "beak" on the one. e.g. Helvetica.
Others have a baseline crossbar on the one, e.g Franklin Gothic.

Nowadays, many typefaces have alternate designs for proportional and tabular "one"s.
I usually put a baseline crossbar on my tab "one"s.

You need to use an OpenType layout palette to access the alternate.