Just curious: PsPad closes and reopens randomly?

U all know that Windows in it's task bar below, adds the programms/window tabs in order they are opened.
But u can drag a tab to another (e.g. first) position, which might beneficial in the case of PsPad, if u have 'some' more applications open (ftp, taski manager, remote access to the server, browser, and another browser, mail-client, file explorer ...), so u can regress to PsPad without doin' a huge search.
So drag it there and PsPad stays there. But a second later it disappears and reappears as the last tab - like if it would have been closed and reopenend.
Workarround: Open at least one more instance of PsPad and it remains on its (e.g. first) posistion.

Do you use current 5.0.4 build?

5.0.4 (531)
But this happens since I swapped over to developer editions (+/- 1/2 a year), and for me there's no problem, because normally I run 2 - 3 instances at once, so they stay where dragged to - it's as I said before: just curious