Will be looking into this later. What I can tell now is that I use this feature myself and I haven't seen the problem you're describing.
How interesting!
I should have said in my first post that the LTD value is actually -1.#IND00, which I understand is negative infinity, although BoincView shows it as 0.00.
I have just done the following to confirm that it is still happening.
Clicked "Resources"
In the resources share block for 3x+1 and milkyway I typed "-"
Clicked "Update"
Both these boxes changed to "0"
Checking my resource share at the 2 projects showed them as "0"
Repeated the above, but typed "100" for 3x+1 and "1000" for milkyway.
The 2 projects now show 100 and 1000 respectively.
For thoroughness I did the same with Opera and got the same result.
Another problem that affects me and not others? (Like my cache problem a little while ago).
Anyway, no rush on this, I've made sure my values are all more than 0 now, and the LTD seems to be adjusting again.
Regards
Rod