I have a bunch of UDFs that I have used for years hundreds of times in
several workbooks. The names of the UDFs in the add-in modules are
coded in mixed case (RayleighMean, RndTallyLog, & ExpSF).

Up until a few days ago, whenever I would code a UDF call in a cell
(=ExpSF(...)), Excel would change the name to lower case
(=expsf(...)). I recall trying repeatedly to get Excel to leave it in
mixed case.

A few days ago, I wrote a new UDF called FmtTime. I just noticed that
all of the calls to this one function are in mixed case just like I
entered them. In fact, if I try to change it to all lower case
(fmttime), Excel changes it back to FmtTime.

What the heck is going on?

Excel is like a lot of girlfriends I've had...can't live with them or
without them.