Are you sure it's the t9 setting and not google maps offering suggestions as you type - like, this is how the program works instead of a glitch? I may be misunderstanding the problem you're having, but when I open the Search box in Google Maps and start typing [I'm in ABC mode], Google Maps shows me Predictive Text underneath the search box. Is this what you're seeing?

Any attempt to turn on t9 on the keyboard fails when I'm in Google Maps...because it seems there's a function already built into the program.

...let me test something else quick and I'll report back...I think I understand a little better the problem youre describing. [Testing and drinking coffee]

OK. I just went into Texts and started typing a message with t9 enabled on the physical keyboard. Everything is ok. Then I opened Google Maps and started to type in the search box. T9 was still enabled and actually worked...recommended words popped up above the keyboard...and Google Maps' own predictive text was displayed. While still in Google Maps, I changed T9 back to ABC...no problems. T9 wasn't on, but Google Mpas continued to provide predictive text.

In the past when T9 mode gets stuck, I try toggling it with the physical keyboard instead of the onscreen. Have you tried that? The more I play with it, the onscreen keyboard seems to be giving me some headaches switching between t9 and abc when in google maps, but toggling it with the physical keyboard clears up the issue.

Try that...unless you did, then I'm at a loss.