I've been using Solidworks since 2006, and there is one behavior that seems to be getting worse. I am using 2014 now.
Sometimes I will be doing a sketch, and the sketch will be fine...constrained, no issues at all... then I trim a line, and the whole thing turns red and becomes unsolvable. I KNOW that I can just "undo" and untrim the line to make it good again, but why should the simple act of trimming a line add some redundant constraint that would create headaches for the user?
A little side note: when I trim and delete lines in sketches in 2014 I am seeing leftover line endpoints as dots all over the place. This didn't used to happen either.
Why does this product seem to somehow seem to get worse in some areas where these problems didn't exist before?
If you trim the center portion out of a line I think it generates a coincident mate between the remaining segments, and if you trim one end away I think it makes a coincident of the remaining line with the point where it used to terminate, so that might overdefine it (although you would expect it to still be able to solve). If that happens I just start deleting the red relations one at a time until it can solve, but start with relations on the line you trimmed.