The program only wants to run once . . .

[RhoSigma]

I might have an idea, do you start the program by hitting F5? If you hold the F5 key too long then the release event of F5 will go to the newly started program, that would trigger the behavior you're describing since the F5 release will be returned by _KeyHit first before the spacebar.

That can't be the case as Steve added a release wait loop in PR #399 to avoid the program is started before F5 is released. That was back in v3.10.0, no idea what version KP is using though.