That was what I thought as well. I suspect it has something to do with my secondary keypad I use for gaming. The odd thing was this just started happening recently and made no changes to my hardware configuration.
The fact that it's a recent issue can come from Ren'Py.
With the 8.x branch and Python 3.x port, a part of the code have been refactored, then ported to the 7.x branch. Gamepad detection/handling can be a part of it.
Then, your secondary keypad is recognized as input, but wrongly interpreted as a gamepad; or not discriminated as not a gamepad, it depend how Ren'Py is coded.
It's totally up to you if you do it or not, but it probably worth trying to unplug the secondary keypad (unless it's a pain in the ass due to configuration issue) next time you face this, just to see if it's actually the cause.
And if it is, perhaps a report to Ren'Py team, on
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