Problem with formatting numbers as text, in Excel 2007

I've got a very strange anomaly going on, in Excel 2007.

It has to do with numbers intended to be formatted as text. Normally, if you want to enter a number formatted as text, you preceed the number with an apostrophe, and Excel interprets that as an intention to store the number as text. When you do this, a little green triangle appears in the upper left corner of the cell, and when you highlight the cell, a little diamond with an '!' mark expands to tell you that the number is stored as text.

However, I've got a spreadsheet with a column on integer numbers which look, on casual examination, to be formatted as text; first of all, the numbers are left-aligned, which is what happens to numbers that are formatted as text. Secondly, when you highlight one of these numbers, and select 'format..'/'format cells...', it shows as text.... yet they aren't actually being interpreted as text, when I access them via my own program (independent of Excel). The only numbers which are being correctly interpreted as text are ones that I entered with the apostrophe....

Another way to format a cell is to highlight the cell, select 'Format...'/'Format cells...', and select 'text' as the format rule.

However, when I try this on a blank spreadsheet, it doesn't work. I enter a number, and it is right-justified, as numbers ordinarily are. If I select the cell, and execute 'Format...'/'Format cells...'/'text', the number becomes left justified.... but it's not really text; no little green triangle, etc.

So, the dilemma is this: why doesn't the 'Format...'/'Format cells...'/'Text' function actually work? Is it possible that there's some sort of optional switch (which I haven't found) that affects the way cell formatting operates?

Anyone?