One of our reports contains a grid where the grid width is set and the width of each column is set and grid width != sum of column widths, so the given constraints are conflicting.
With the latest release 2.1.2 of our (patched) version of BIRT, the behavior changed in comparsion to an (unreleased) release based on BIRT 4.10.

The only code change which comes to my mind as an explanation is the Fix for line-height < 100% bug
triestram-partner@d65522c

I won't say this is an regression bug, because this conflicting contraints are really an edge case, but it is an unexpected (at least for me) behavior change.