Sexual discrimination or not?

[OttifantSir]

I have just watched a news cast that made me think a bit. As this case is probably very country-specific to Norway, I list this here instead of in the Politics forum:

A substitute worker in our country has the right to get a tenure if that sub has been filling the same position for four years or more.

A mother has the right to take an extended, paid, leave of absence after she has given birth.

The specifics of this case was this: A female substitute teacher had been working a while in her position when she gave birth. She took the extended leave of absence. Now she has been working again for some time, reaching the limit of four years or more needed to be granted a tenure. But the employer, in this case the commune/county says she has to work nine more months to be eligible for tenure due to her leave of absence since the first rule says she has to have been performing her duties continuously for four years. Obviously she hasn't done this, so on one hand she isn't being discriminated (in the legal sense), on the other hand, she has been employed for four years, so she is eligible for tenure.

It really made me think. Is this really a case of the decision-makers seeing her as a substitute (filling in for one worker) then taking an extended leave of absence (creating the need for yet another substitute) and fearing that they might end up in this situation once more, therefore saying she has to catch up with her employment record/work an additional nine months to be eligible for tenure just to be sure they get what they pay for? Or is it just plain and simple old-fashioned thinking that women shouldn't be working?

However, my question to this forum is: Do you see this as being discrimination, or just common sense?

I see both sides of this case, but I am unable to make up a decision on it.