Bisect gave this commit as culprit:
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commit f7855cae5e5d4e0ddc552cd6785119bb47c81d44
Author: Nicolas Pomarede <npomarede@xxxxxxxxxxxx>
Date:   Thu Sep 12 22:18:44 2019 +0200
     For the blitter, use x_count to decide to add src_x_incr or 
src_y_incr after reading each src word
     We use the same conditions as described in the blitter 
documentation, instead of handling
     an additional variable to count the number of reads
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Reverting that patch, fixes fonts in TOS v4 desktop.