I have had this problem as well. When I enter a list of numbers in a AAA1111 format, and a value happens to be something like;
JUN4826 or JUL3892
it turns into
Jun-26 or JUL-92
Which are recognized as the values
07/01/4826 or 07/01/3892
Resulting in the numeric values
1068883 or 727747

Which is really annoying.

One way around it is to format the entire column as TEXT before entering the data, and if copying data from another sheet make sure you Paste Special / Values

OR, you can place a ' before the string

'1/4 will show in the cell as 1/4 regardless of format


Edit: Sorry, didn't notice this was in the VBA section. See above responses!