This bug is probably related to https://bugs.freedesktop.org/show_bug.cgi?id=41304 and https://bugs.freedesktop.org/show_bug.cgi?id=41915 but it is not a duplicate.
Whenever a formula is being edited, the color coding disappears.
Type "=A1" into a cell and press the enter key. Now double click the cell and notice that "A1" is highlighted in color. When you now enter anything after "A1" (e.g. whitespace or comma), the color coding will disappear and leave the formula in all black. This is very annoying, especially with long formulas.
Thanks for bugreport. Indeed, very unhandy.
reproduced in 3.3.4 and 3.5.4 on Fedora 64 bit
reproducible when cursor in FormulaBar and when in cell
changing version to 3.3.4 as most early reproduced
*** This bug has been marked as a duplicate of bug 38304 ***