for the last year i've using my mamaiya tlr, prior to that it was my 645 pro tl with winder. i never had a battery die. i know i did leave it on but i don't remember length of time. i replaced the battery once a year - never had a problem.
so yes, weird... if someone doesn't chime in with more info i would buy 2 more batteries and try to make it fail, to check it out. good luck.
On the shelf camera batteries like the 2CR5 are more prone to being older stock than they used to be.
I would inspect the contacts in the battery compartment, but otherwise try another battery.
The shutter uses the same in-body battery as the meter, not the winder battery. Otherwise you couldn't use the camera without the winder. I used lithium 2cr5 batteries in the winder and those lasted a long time. But leaving the winder on should not drain the battery.