"keepITcool" wrote
the isdate function's description from vba help..
Returns a Boolean value indicating whether an expression
can be converted to a date.
the crux is in the word CAN..

....excepting in this case it can't be displayed (visually) as a date -
although it does not cause an exception so I guess that meets the CAN
criteria!

plus there are some differences between VBA and Excel functions.

Understood - however it was the VBA giving me the heartburn.

I ran a few loops (swapping system separators)
and determined that vba's string interpretation is based on ALL
of the following user's locale settings...
listseparator,decimalseparator,dateseparator,hours eparator
(optionally including the am pm indicators..)

Yuk!

funny as you'd expect it to be based on either
locale's or usenglish Date separator.

I agree. It looks like an each way bet being placed - I presume somehow in
response to something like (as I understand them) the European formats for
dates like yyyy.mm.dd and decimal numbers like 999.999.999,99 ie. the same
char being used in different contexts.

The Q214233 article mentions in respect of dates
a.. If a number contains a slash mark (/) or hyphen (-), it may be
converted to a date format.
It isn't nearly as comprehensive as your research shows it needs to be in
respect of commas etc!

also see harlan grove's article "an interesting read"

It was very interesting! As it happens I have a B.Sc majoring in Zoology
and the risk this trait poses for genetic analysis is not lost on me! I'll
bet the smart alec's that though they would help us all out by casting
"likely" dates etc didn't see this one coming! Do you know if there is any
way to disable this "feature" without having to go to the lengths of
preformatting the cell?

Cheers
Frank.