Comment 32 for bug 150709

Since your ddcprobe output has only one "dtiming" entry at "1280x1024@99" we can consider it a driver bug not to choose it automatically:

"The VESA E-EDID Standard requires that the First Detailed Timing Descriptor be the “preferred” video format and subsequent detailed timing descriptors listed in order of decreasing preference."

However it doesn't extract those timings, and you don't have a 99Hz modeline.