When I try to name a track in the Classic Tracks Window, if I try to type the letter 'p', it doesn't get typed. Instead, some weird thing happens in the Bars window - the column of that bar turns blue and I get a "1a" at the top of the column. If I press 'p' again (presumably because I'm still trying to type it and it didn't come up!), the indicator changes to "1b" and the column turns green. A third press makes it go back to normal, but I still don't have the letter 'p' in my track name.

As you might imagine, this makes it difficult to type names such as "Soprano" or "Tympani".

What is happening, and how can I turn it off, please?