Decreasing lag time does not make start date earlier

[obrady]

Hello,

I have a project with a number of tasks linked with start-to-start lag
times. The problem is however, that decreasing the lag time of a task
will not make the start date earlier, except for first task to have a
lag time link.
Increasing the lag time does result in the start date of a task being
later, and once you have done this you cannot get it earlier again, even
if you set the lag time back to what it orginally was.

A little diagram to help make my issue clearer:

Task 1. Stage 1 starts 4/5/09
Task 2. Stage 1a starts 4/5/09
Task 3. Stage 1b starts 11/5/09 predecessor 2SS+5
Task 4. Stage 1c starts 25/5/09 predecessor 3SS+10

If I change Task 3's predecessor to 2SS+2, it moves the start date back
correctly. But if I change Task 4's predecessor to 3SS+5 it will not
change the start date. If I change the predecessor to 3SS+15 it will
change the start date, but then I can't get it back to the original
again!

I have made sure that auto calculation is turned on and made sure there
are no constraints by setting everything to "As Soon As Possible". Is
there anything else I can check to find out what is forcing these dates
the way they are?

Thanks for any help you can provide.

 

[Dave]

It works correctly for me on Project 2003. What version are you using?

Do you have resources assigned to these tasks? Is auto-levelling turned on?

If you reduce the lag can you 'drag' the task back?

 

[obrady]

Thanks for your reply. It turned out to be an issue with mismatched
project start dates in the subproject files. Once they were all set
correctly everything started working correctly again.